Remove unused admin group view for LDAP sync

Over 2 years ago an errant change resulted in LDAP sync settings
no longer being shown in the admin area when editing a group.
Since its been such a long time since the feature worked, and we
haven't heard from users that they're missing this feature, it
can be removed. There are many other group settings not available
in admin area, too.

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

@@ -36,5 +36,3 @@
     .form-actions
       = f.submit _('Save changes'), class: "btn btn-success", data: { qa_selector: 'save_changes_button' }
       = link_to  _('Cancel'), admin_group_path(@group), class: "btn btn-cancel"
-
-= render_if_exists 'ldap_group_links/ldap_syncrhonizations', group: @group

ee/app/views/ldap_group_links/_ldap_group_links_synchronizations.html.haml

-- group = local_assigns.fetch(:group)
-- return unless Gitlab::Auth::Ldap::Config.group_sync_enabled? && group.persisted?
-
-%h3.page-title LDAP synchronizations
-= render 'ldap_group_links/form', group: group
-= render 'ldap_group_links/ldap_group_links', group: group