wayland: Propagate a tablet's DEVICE_REMOVED to trigger the signals
Clutter's "device-removed" signal is sent in clutter_seat_handle_event_post(). Our tablet code is set up to handle that signal to then notify wayland clients of removed tablet devices.
However, returning CLUTTER_EVENT_STOP for a DEVICE_REMOVED event means we never get to the point where we send out the signals and thus never remove the tablets.
Closes #3615 (closed)