Update alarm_unregister_processing_queue() to cancel scheduled alarms

Update the alarm_unregister_processing_queue() implementation
so it cancels all alarms that are scheduled on the corresponding
queue.
This fixes a race condition during Bluetooth shutdown: if an alarm
expires right after an alarm processing queue is invalidated,
the alarm processing would try to use the invalidated queue.

Added the corresponding unit tests.

Also, added a missing call to alarm_unregister_processing_queue().

Bug: 26982349
Change-Id: I09a111e8080b6dbc354dffa03a487f7a8c578ce6