Remove unused form for admin application settings

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/admin/application_settings/_form.html.haml

-= form_for @application_setting, url: admin_application_settings_path, html: { class: 'form-horizontal fieldset-form' } do |f|
-  = form_errors(@application_setting)
-
-  .form-actions
-    = f.submit 'Save', class: 'btn btn-save'

app/views/admin/application_settings/show.html.haml

@@ -302,6 +302,3 @@
       = _('Allow requests to the local network from hooks and services.')
   .settings-content
     = render 'outbound'
-
-.prepend-top-20
-  = render 'form'