APC: Remove the MUTE_BY_UNKNOWN flag

This flag can be misleading. Also it is not false to set the value to 0
when a player has not had an active mute event. For anonymization using
also the 0 value.

Test: dumpsys audio & atest android.media.audio.cts.AudioPlaybackConfigurationTest
Bug: 257136556
Change-Id: Ie8579f1824e4a514c437fc0e25891d46783c388e