bass: Collect and remove sources while stopping receivers

Remove source method can try to remove group managed source before
marking them as paused. Sources first have to be marked as paused if
needed then removed.

Tag: #feature
Test: atest LeAudioServiceTest LeAudioBroadcastServiceTest
Bug: 298080973
Bug: 308171251
Change-Id: Ied9a53f3d301a42d8c51a257bd05f45c1223ea3e