Move scheduled alarm scrub off main thread

We currently do a database update when the "boot completed" intent
is received.  Doing it on the main thread appears to be causing ANRs,
so this moves it to a background thread.  An "empty" service is
used to discourage the system from killing the provider while this
is in progress.

Also, removed an unused field from CalendarAlarmManager.

Bug 5262151

Change-Id: I8e5b1bd7782500e1827f43d7a453f824a1e7944c
4 files changed