Updater: Don't show delete twice

* If an update exists and can be deleted, the action button AND the
  popup menu both show the delete action
* By checking wether the action already shows "Delete" we can hide
  that action from the submenu
* Additionally check for online availability to only hide it when it's
  not the last item - otherwise a click on the menu icon wouldn't do
  anything

Change-Id: Idc5da3962be4e0a69847f47b3c5f014b251bd438