Update A2dpServiceTest to expect state machine removal with unbond

aosp/3381766 ensures that A2DP state machine is removed when the bond is
removed. A2dpServiceTest has to be updated to match the new behaviour.

Test: atest A2dpServiceTest
Flag: com.android.bluetooth.flags.a2dp_cleanup_on_remove_device
Bug: 339763326
Bug: 381313622
Change-Id: I46bd3ff4feacf3ce03196b5a6d12945f0eff3b16