Remove Handler messages on QSTileImpl destroy

This prevents the tiles from being reference kept (as the MessageQueue
will have a reference to it). In particular, because
QSTileImpl#handleStale kepts rescheduling, this will never be collected.

Fixes: 146151014
Test: atest QSTileImpl
Change-Id: I0120953ae7e457a941dbebfcfd5da9dce9c09adb