Fix restore notifications from admins page

The restore feature was not working properly. When pushed, the button
was removing the notification from the admins panel, but it was not
restoring in the proposal.

I added an `after_restore` function (that I missed in the first PR)
so that the notification is unmarked as moderated.

spec/features/admin/proposal_notifications_spec.rb

@@ -25,6 +25,7 @@ feature 'Admin proposal notifications' do
 
     expect(proposal_notification.reload).not_to be_hidden
     expect(proposal_notification).to be_ignored
+    expect(proposal_notification).not_to be_moderated
   end
 
   scenario 'Confirm hide' do