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/pyunit.vim b/runtime/compiler/pyunit.vim
index 2a4ea92..2368346 100644
--- a/runtime/compiler/pyunit.vim
+++ b/runtime/compiler/pyunit.vim
@@ -2,15 +2,12 @@
 " Compiler:	Unit testing tool for Python
 " Maintainer:	Max Ischenko <mfi@ukr.net>
 " Last Change: 2004 Mar 27
+"		2024 Apr 03 by The Vim Project (removed :CompilerSet definition)
 
 if exists("current_compiler")
   finish
 endif
 let current_compiler = "pyunit"
 
-if exists(":CompilerSet") != 2		" older Vim always used :setlocal
-  command -nargs=* CompilerSet setlocal <args>
-endif
-
 CompilerSet efm=%C\ %.%#,%A\ \ File\ \"%f\"\\,\ line\ %l%.%#,%Z%[%^\ ]%\\@=%m