Backport support for finding EE workers

This backports support for finding EE workers in ee/app/workers from EE
to CE, since we already do this for the configuration paths constant.
This removes the need for EE specific modules.

lib/gitlab/sidekiq_config.rb

@@ -48,7 +48,9 @@ module Gitlab
     end
 
     def self.workers
-      @workers ||= find_workers(Rails.root.join('app', 'workers'))
+      @workers ||=
+        find_workers(Rails.root.join('app', 'workers')) +
+        find_workers(Rails.root.join('ee', 'app', 'workers'))
     end
 
     def self.find_workers(root)