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/decada.vim b/runtime/compiler/decada.vim
index 0bf5487..11b0cb4 100644
--- a/runtime/compiler/decada.vim
+++ b/runtime/compiler/decada.vim
@@ -14,6 +14,7 @@
 "               08.09.2006 MK Correct double load protection.
 "    Help Page: compiler-decada
 "------------------------------------------------------------------------------
+" Last Change:	2024 Apr 03 by The Vim Project (removed :CompilerSet definition)
 
 if (exists("current_compiler") && current_compiler == "decada") || version < 700
    finish
@@ -34,13 +35,6 @@
    call g:decada.Set_Session ()
 endif
 
-if exists(":CompilerSet") != 2
-   "
-   " plugin loaded by other means then the "compiler" command
-   "
-   command -nargs=* CompilerSet setlocal <args>
-endif
-
 execute "CompilerSet makeprg="     . escape (g:decada.Make_Command, ' ')
 execute "CompilerSet errorformat=" . escape (g:decada.Error_Format, ' ')