Fixes side effects with application_controller_patch

Requiring ApplicationController:

`require 'application_controller`

may lead to side effects under certain circumstances (see xmera Circle
issue 1444).

Since the code runs even without the requirement above in
redmine_message_customize/lib/message_customize/application_controller_patch.rb
the line is deleted.

Author: liaham

lib/message_customize/application_controller_patch.rb

@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-require 'application_controller'
-
 module MessageCustomize
   module ApplicationControllerPatch
     def self.included(base)