[SB] Remove flag status_bar_show_audio_only_projection_chip

Flag launched awhile ago, so we can remove it.

Fixes: 409607621
Bug: 373308507
Flag: EXEMPT flag removal

Test: atest MediaProjectionManagerRepositoryTest
MediaProjectionChipInteractorTest
Test: share just audio with an app -> verify chip with no timer still appears
Test: share screen with app -> verify chip with timer appears

Change-Id: I2c01e8757643d233482bc1dead0f0c74efd4c785