[iOS] Revert to using AVAudioSession for determining the default microphone
<rdar://problem/113404912>
Pull request: https://github.com/WebKit/WebKit/pull/21194
Committed 271454@main (25e1940919d2): <https://commits.webkit.org/271454@main> Reviewed commits have been landed. Closing PR #21194 and removing active labels.