Remove most traces of WinHelp support.

Remove the 'winhelp-topic' IDs from the Halibut source, and from the
code. Now we have one fewer name to think of every time we add a
setting.

I've left the HELPCTX system in place, with the vague notion that it
might be a useful layer of indirection for some future help system on a
platform like Mac OS X.

(I've left the putty.hlp target in doc/Makefile, if nothing else because
this is a convenient test case for Halibut's WinHelp support. But the
resulting help file will no longer support context help.)

doc/errors.but

@@ -13,8 +13,6 @@ bug (see \k{feedback}) and we will add documentation for it.
 \H{errors-hostkey-absent} \q{The server's host key is not cached in
 the registry}
 
-\cfg{winhelp-topic}{errors.hostkey.absent}
-
 This error message occurs when PuTTY connects to a new SSH server.
 Every server identifies itself by means of a host key; once PuTTY
 knows the host key for a server, it will be able to detect if a
@@ -36,8 +34,6 @@ See \k{gs-hostkey} for more information on host keys.
 
 \H{errors-hostkey-wrong} \q{WARNING - POTENTIAL SECURITY BREACH!}
 
-\cfg{winhelp-topic}{errors.hostkey.changed}
-
 This message, followed by \q{The server's host key does not match
 the one PuTTY has cached in the registry}, means that PuTTY has
 connected to the SSH server before, knows what its host key
@@ -144,8 +140,6 @@ from the error message box.
 \H{errors-cant-load-key} \q{Unable to use this private key file},
 \q{Couldn't load private key}, \q{Key is of wrong type}
 
-\cfg{winhelp-topic}{errors.cantloadkey}
-
 Various forms of this error are printed in the PuTTY window, or
 written to the PuTTY Event Log (see \k{using-eventlog}) when trying
 public-key authentication, or given by Pageant when trying to load a

doc/pageant.but

@@ -1,7 +1,5 @@
 \C{pageant} Using \i{Pageant} for authentication
 
-\cfg{winhelp-topic}{pageant.general}
-
 Pageant is an SSH \i{authentication agent}. It holds your \i{private key}s
 in memory, already decoded, so that you can use them often
 \I{passwordless login}without needing to type a \i{passphrase}.
@@ -58,8 +56,6 @@ existing keys.
 
 \S{pageant-mainwin-keylist} The key list box
 
-\cfg{winhelp-topic}{pageant.keylist}
-
 The large list box in the Pageant main window lists the private keys
 that are currently loaded into Pageant. The list might look
 something like this:
@@ -87,8 +83,6 @@ applied to your \c{authorized_keys} file.
 
 \S{pageant-mainwin-addkey} The \q{Add Key} button
 
-\cfg{winhelp-topic}{pageant.addkey}
-
 To add a key to Pageant by reading it out of a local disk file,
 press the \q{Add Key} button in the Pageant main window, or
 alternatively right-click on the Pageant icon in the system tray and
@@ -109,8 +103,6 @@ also add one from a remote system by using agent forwarding; see
 
 \S{pageant-mainwin-remkey} The \q{Remove Key} button
 
-\cfg{winhelp-topic}{pageant.remkey}
-
 If you need to remove a key from Pageant, select that key in the
 list box, and press the \q{Remove Key} button. Pageant will remove
 the key from its memory.

doc/pgpkeys.but

@@ -1,7 +1,5 @@
 \A{pgpkeys} PuTTY download keys and signatures
 
-\cfg{winhelp-topic}{pgpfingerprints}
-
 \I{verifying new versions}We create \i{GPG signatures} for all the PuTTY
 files distributed from our web site, so that users can be confident
 that the files have not been tampered with. Here we identify

doc/pubkey.but

@@ -61,8 +61,6 @@ The key types supported by PuTTY are described in \k{puttygen-keytype}.
 
 \H{pubkey-puttygen} Using \i{PuTTYgen}, the PuTTY key generator
 
-\cfg{winhelp-topic}{puttygen.general}
-
 PuTTYgen is a key generator. It \I{generating keys}generates pairs of
 public and private keys to be used with PuTTY, PSCP, and Plink, as well
 as the PuTTY authentication agent, Pageant (see \k{pageant}).  PuTTYgen
@@ -106,8 +104,6 @@ server to accept it.
 
 \S{puttygen-keytype} Selecting the type of key
 
-\cfg{winhelp-topic}{puttygen.keytype}
-
 Before generating a key pair using PuTTYgen, you need to select
 which type of key you need. PuTTYgen currently supports these types
 of key:
@@ -133,8 +129,6 @@ supported by PuTTY are RSA, DSA, ECDSA, and Ed25519.
 
 \S{puttygen-strength} Selecting the size (strength) of the key
 
-\cfg{winhelp-topic}{puttygen.bits}
-
 The \q{Number of bits} input box allows you to choose the strength
 of the key PuTTYgen will generate.
 
@@ -149,8 +143,6 @@ equivalent security to RSA with smaller key sizes.)
 
 \S{puttygen-generate} The \q{Generate} button
 
-\cfg{winhelp-topic}{puttygen.generate}
-
 Once you have chosen the type of key you want, and the strength of
 the key, press the \q{Generate} button and PuTTYgen will begin the
 process of actually generating the key.
@@ -177,8 +169,6 @@ appear in the window to indicate this.
 
 \S{puttygen-fingerprint} The \q{\ii{Key fingerprint}} box
 
-\cfg{winhelp-topic}{puttygen.fingerprint}
-
 The \q{Key fingerprint} box shows you a fingerprint value for the
 generated key. This is derived cryptographically from the \e{public}
 key value, so it doesn't need to be kept secret; it is supposed to
@@ -193,8 +183,6 @@ utility, will list key fingerprints rather than the whole public key.
 
 \S{puttygen-comment} Setting a comment for your key
 
-\cfg{winhelp-topic}{puttygen.comment}
-
 If you have more than one key and use them for different purposes,
 you don't need to memorise the key fingerprints in order to tell
 them apart. PuTTYgen allows you to enter a \e{comment} for your key,
@@ -213,8 +201,6 @@ PuTTYgen, change the comment, and save it again.
 
 \S{puttygen-passphrase} Setting a \i{passphrase} for your key
 
-\cfg{winhelp-topic}{puttygen.passphrase}
-
 The \q{Key passphrase} and \q{Confirm passphrase} boxes allow you to
 choose a passphrase for your key. The passphrase will be used to
 \i{encrypt} the key on disk, so you will not be able to use the key
@@ -258,8 +244,6 @@ a result.
 
 \S{puttygen-savepriv} Saving your private key to a disk file
 
-\cfg{winhelp-topic}{puttygen.savepriv}
-
 Once you have generated a key, set a comment field and set a
 passphrase, you are ready to save your private key to disk.
 
@@ -274,8 +258,6 @@ will need to tell PuTTY to use for authentication (see
 
 \S{puttygen-savepub} Saving your public key to a disk file
 
-\cfg{winhelp-topic}{puttygen.savepub}
-
 RFC 4716 specifies a \I{SSH-2 public key format}standard format for
 storing SSH-2 public keys on disk. Some SSH servers (such as
 \i\cw{ssh.com}'s) require a public key in this format in order to accept
@@ -300,8 +282,6 @@ public keys.
 \S{puttygen-pastekey} \q{Public key for pasting into \i{authorized_keys
 file}}
 
-\cfg{winhelp-topic}{puttygen.pastekey}
-
 All SSH-1 servers require your public key to be given to it in a
 one-line format before it will accept authentication with your
 private key. The \i{OpenSSH} server also requires this for SSH-2.
@@ -317,8 +297,6 @@ public-key authentication once you have generated a key.
 
 \S{puttygen-load} Reloading a private key
 
-\cfg{winhelp-topic}{puttygen.load}
-
 PuTTYgen allows you to load an existing private key file into
 memory. If you do this, you can then change the passphrase and
 comment before saving it again; you can also make extra copies of
@@ -337,8 +315,6 @@ for information about importing foreign key formats.
 
 \S{puttygen-conversions} Dealing with private keys in other formats
 
-\cfg{winhelp-topic}{puttygen.conversions}
-
 Most SSH-1 clients use a standard format for storing private keys on
 disk. PuTTY uses this format as well; so if you have generated an
 SSH-1 private key using OpenSSH or \cw{ssh.com}'s client, you can use

doc/using.but

@@ -620,8 +620,6 @@ use the \c{-load} option (described in \k{using-cmdline-load}).
 
 \S{using-cleanup} \i\c{-cleanup}
 
-\cfg{winhelp-topic}{options.cleanup}
-
 If invoked with the \c{-cleanup} option, rather than running as
 normal, PuTTY will remove its \I{removing registry entries}registry
 entries and \i{random seed file} from the local machine (after