Differences between protocols: remove the entire paragraph about environment

variables. It was no longer true (given that we support them in SSH-2 now),
and the new situation was probably too complex to explain in an introductory
chapter. And the utility of setting them seems to be marginal these days given
the lack of server support.

[originally from svn r4679]

doc/intro.but

@@ -1,4 +1,4 @@
-\versionid $Id: intro.but,v 1.6 2004/06/15 11:00:28 jacob Exp $
+\versionid $Id: intro.but,v 1.7 2004/10/24 15:58:31 jacob Exp $
 
 \C{intro} Introduction to PuTTY
 
@@ -66,14 +66,6 @@ high-security protocol. It uses strong cryptography to protect your
 connection against eavesdropping, hijacking and other attacks. Telnet
 and Rlogin are both older protocols offering minimal security.
 
-\b Telnet allows you to pass some settings on to the server, such as
-environment variables. (These control various aspects of the
-server's behaviour. You can usually set them by entering commands
-into the server once you're connected, but it's easier to have
-Telnet do it automatically.) SSH and Rlogin do not support this.
-However, most modern Telnet servers don't allow it either, because
-it has been a constant source of security problems.
-
 \b SSH and Rlogin both allow you to log in to the server without
 having to type a password. (Rlogin's method of doing this is
 insecure, and can allow an attacker to access your account on the