Various fixes and improvements (#12878)

* Fix unused role routes being generated

* Remove unused JavaScript code

* Refactor filters code to be DRYer

* Fix `.count == 0` comparisons to `.empty?` in views

* Fix filters in views

app/views/settings/applications/index.html.haml

@@ -4,7 +4,7 @@
 - content_for :heading_actions do
   = link_to t('doorkeeper.applications.index.new'), new_settings_application_path, class: 'button'
 
-- if @applications.count == 0
+- if @applications.empty?
   %div.muted-hint.center-text=t 'doorkeeper.applications.index.empty'
 - else
   .table-wrapper