Remove calls to client while holding lock

The dispatchPlaybackConfigChange callback could cause a deadlock in
case the client is running in the same process as the AudioService and
at the same time it's unregistering a client while a dispatch is active.

Test: CtsMediaAudioTestCases and dumpsys audio
Bug: 227596824
Change-Id: I6c6c13e254cb048aebc63cb594b0c4658cf86b91