Make messcompat.el obsolete.

* lisp/obsolete/messcompat.el: Move here from lisp/gnus.
* doc/misc/message.texi (Compatibility): Remove section.

doc/misc/message.texi

@@ -67,7 +67,6 @@ Message mode buffers.
 * Interface::         Setting up message buffers.
 * Commands::          Commands you can execute in message mode buffers.
 * Variables::         Customizing the message buffers.
-* Compatibility::     Making Message backwards compatible.
 * Appendices::        More technical things.
 * GNU Free Documentation License:: The license for this documentation.
 * Index::             Variable, function and concept index.
@@ -2587,22 +2586,6 @@ An @dfn{action} can be either: a normal function, or a list where the
 a form to be @code{eval}ed.
 
 
-@node Compatibility
-@chapter Compatibility
-@cindex compatibility
-
-Message uses virtually only its own variables---older @code{mail-}
-variables aren't consulted.  To force Message to take those variables
-into account, you can put the following in your @file{.emacs} file:
-
-@lisp
-(require 'messcompat)
-@end lisp
-
-This will initialize many Message variables from the values in the
-corresponding mail variables.
-
-
 @node Appendices
 @chapter Appendices
 

lisp/obsolete/messcompat.el

@@ -4,6 +4,7 @@
 
 ;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
 ;; Keywords: mail, news
+;; Obsolete-since: 25.2
 
 ;; This file is part of GNU Emacs.