Call stopSelfWhenDone() *after* canceling the notification.

When a bugreport is shared it's necessary to remove its system notification and
stop the service if there is no more pending bugreports. Since the
service will might be killed as a result, to call to cancel the
notification must be done prior to calling stopSelf().

BUG: 27524556
Change-Id: Iae9a263b6cee0e4a0a7df3e52621e56b50983fec