Remove documentation for "Out of space for port forwardings" error.

It no longer exists in the code, and should have been obsoleted by
r9214 at the latest.

[originally from svn r9626]
[r9214 == a1f3b7a358adaa7c2a98359cd0373aa823eeb14b]

doc/errors.but

@@ -1,4 +1,4 @@
-\define{versioniderrors} \versionid $Id$
+s\define{versioniderrors} \versionid $Id$
 
 \C{errors} Common \i{error messages}
 
@@ -58,20 +58,6 @@ in the same way as you would if it was new.
 
 See \k{gs-hostkey} for more information on host keys.
 
-\H{errors-portfwd-space} \q{Out of space for port forwardings}
-
-PuTTY has a fixed-size buffer which it uses to store the details of
-all \i{port forwardings} you have set up in an SSH session. If you
-specify too many port forwardings on the PuTTY or Plink command line
-and this buffer becomes full, you will see this error message.
-
-We need to fix this (fixed-size buffers are almost always a mistake)
-but we haven't got round to it. If you actually have trouble with
-this, let us know and we'll move it up our priority list.
-
-If you're running into this limit, you may want to consider using
-dynamic port forwarding instead; see \k{using-port-forwarding}.
-
 \H{errors-cipher-warning} \q{The first cipher supported by the server is
 ... below the configured warning threshold}