Remove FLAG_SCO handling from the AudioAttributes

Now that we removed STREAM_BLUETOOTH_SCO internally within the
AudioService we want to make sure that the AudioAttributes will not be
mapped to AUDIO_STREAM_BLUETOOTH_SCO on the native layers which are not
initialized properly.

Test: manual
Bug: 376756660
Flag: EXEMPT bugfix
Change-Id: I60de6fa9ae7de5619e5735a072732aa5cac44c87