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/dotnet.vim b/runtime/compiler/dotnet.vim
index ac64084..1290357 100644
--- a/runtime/compiler/dotnet.vim
+++ b/runtime/compiler/dotnet.vim
@@ -2,6 +2,7 @@
 " Compiler:            dotnet build (.NET CLI)
 " Maintainer:          Nick Jensen <nickspoon@gmail.com>
 " Last Change:         2022-12-06
+"                      2024 Apr 03 by The Vim Project (removed :CompilerSet definition)
 " License:             Vim (see :h license)
 " Repository:          https://github.com/nickspoons/vim-cs
 
@@ -10,10 +11,6 @@
 endif
 let current_compiler = "dotnet"
 
-if exists(":CompilerSet") != 2		" older Vim always used :setlocal
-  command -nargs=* CompilerSet setlocal <args>
-endif
-
 let s:cpo_save = &cpo
 set cpo&vim