Removed order from sub-query projects for search

There's no need to order queries used as sub-queries and doing so can
add potential overhead.

lib/gitlab/search_results.rb

@@ -94,7 +94,7 @@ module Gitlab
     end
     def project_ids_relation
-      limit_projects.select(:id)
+      limit_projects.select(:id).reorder(nil)
     end
   end
 end