Clean up dead RouterRecords after unbinding them

When apps are force killed or the ActivityManager freezes apps and kill
apps unexpectly, some RouterRecords are not cleaned up and their
media route providers might still have route controller instances
running, which might sent updates to the media router framework to
update status to dead routers. In this case, we have a lot of
DeadObjectException errors. Even worse, if there is an active casting
session when the app is force killed, the previous casting session
might interrupt the following casting session. In other words, we can't
cast to a remote device if the previous casting session was ended
unexpectly. Thus, cleaning up the dead RouterRecords is necessary
to ensure smooth casting experience.

Flag: com.android.media.flags.clean_up_dead_router_records_after_unbinding
Test: presubmit and manually tested with demo app
Bug: b/414836668
Fix: b/414836668
Change-Id: Ide8f369a237cd9c2dc7d51c160ad263c602496e3