Unregister listeners and reset wake lock

The ContentProvider might be recreated by the system, so we it's
not necessarily a singleton. We need to cleanup listener registration
and alarms before reattributing the static variable.

Change-Id: I07aec96e77c67d96d31c7e38c85f5ce6f5ef2216
Merged-In: I9bc993f372a8c05258f1778eb3d415af04544714
Fixes: 135344397
Fixes: 135582651
Test: bind and unbind slice various times
Test: atest KeyguardSliceProviderTest