Don't allow concurrent starts and stops and clean up receiver

We were getting an non-trivial amount of exceptions surrounding the MAP
client broadcast receiver unregistration. These typically come from
unregistering something thats null, not registered, or already
unregistered.

This change makes the start/stop process atomic so we don't have any
registration race conditions. It also makes it so we wont be able to
unregister the same thing twice.

Bug: b/152632559
Test: Build, flash, atest
Change-Id: I277a4799d4ba5328560ec75e5e6d8743d1c511cd
Merged-In: I277a4799d4ba5328560ec75e5e6d8743d1c511cd