Bass: Remove sink broadcast metadata in remove source after disconnect

Follow up on "Add support for multiple sources per sink device"

After each removal of sink metadata, the entire group should be checked,
as there is a possibility that some sinks were disconnected earlier and
their sink metadata was retained.

Bug: 385389212
Flag: EXEMPT, day-to-day bugfix covered by unit tests
Test: atest BassClientServiceTest
Change-Id: I3c76cc185675d29277ed4abc11f24029d32a05d0