Do not use isAudioOn hidden API

Instead we can use BluetoothHeadset.getConnectedDevices and check the
size of the list. This is the same behavior (actually isAudioOn would
have included connecting devices, but we don't include that because we
shouldn't)

Bug: 137202333
Test: manual
Change-Id: I928c5a2e944b74559304ad9337a8d02a59721492
1 file changed