Use ApplicationSetting.current in Admin::ApplicationSettingsController

See merge request gitlab-org/gitlab-ee!3323

Backported as part of authorized_keys in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/16014

app/controllers/admin/application_settings_controller.rb

@@ -52,7 +52,7 @@ class Admin::ApplicationSettingsController < Admin::ApplicationController
   private
 
   def set_application_setting
-    @application_setting = current_application_settings
+    @application_setting = ApplicationSetting.current
   end
 
   def application_setting_params