AudioService: restore A2DP/wired headset auto selection

Restore automatic routing behavior when wired headset or BT headset
is connected.
This behavior was changed by commit 0234587b
This change mostly reverts 0234587b but keeps public methods
setBluetoothA2dpOn() and isBluetoothA2dpOn() deprecated with
stub implementations.

Bug: 30963785
Bug: 31424965
Change-Id: I90ea04584df595a778993595ad0076fef809ed98