runtime: Remove fallback :CompilerSet definition from compiler plugins

The :CompilerSet command was added in version Vim 6.4 which was released
twenty years ago.  Other runtime files do not support versions of that
vintage so it is reasonable to remove this fallback command definition
now.

closes: #14399

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/compiler/mcs.vim b/runtime/compiler/mcs.vim
index 94a1848..4d94f47 100644
--- a/runtime/compiler/mcs.vim
+++ b/runtime/compiler/mcs.vim
@@ -3,6 +3,7 @@
 " Maintainer:   Jarek Sobiecki <harijari@go2.pl>
 " Contributors: Peter Collingbourne and Enno Nagel
 " Last Change:  2024 Mar 29
+"		2024 Apr 03 by The Vim Project (removed :CompilerSet definition)
 
 if exists("current_compiler")
   finish