Remove uninstalled apps from the SLS list of enabled apps.

This installs a broadcast receiver in the CommunalManager system
service, so that we keep the array of packages in Settings up-to-date
with package removals.

Test: locally on device
Test: atest FrameworksMockingServicesTests:CommunalManagerServiceTest
Bug: 200324021
Change-Id: I227958736b3fe3ccefa32531eda88dfe251494c4