Clean up admin UI for accounts (#6004)

* Add staff filter to admin UI for accounts, remove obsolete columns

* Only display OStatus section in admin UI for accounts when OStatus data

app/views/admin/accounts/index.html.haml

@@ -30,6 +30,11 @@
           = filter_link_to t('admin.accounts.moderation.suspended'), {suspended: nil}, {suspended: '1'}
         - else
           = filter_link_to t('admin.accounts.moderation.suspended'), suspended: '1'
+  .filter-subset
+    %strong= t('admin.accounts.role')
+    %ul
+      %li= filter_link_to t('admin.accounts.moderation.all'), staff: nil
+      %li= filter_link_to t('admin.accounts.roles.staff'), staff: '1'
   .filter-subset
     %strong= t('admin.accounts.order.title')
     %ul
@@ -56,9 +61,7 @@
       %tr
         %th= t('admin.accounts.username')
         %th= t('admin.accounts.domain')
-        %th= t('admin.accounts.protocol')
-        %th= t('admin.accounts.confirmed')
-        %th= fa_icon 'paper-plane-o'
+        %th
         %th
     %tbody
       = render @accounts