BluetoothDeviceManager: Fix regression after gtbs merge

Code incorretly removed all active devices when it disconnects audio.
This patch brings previous behaviour and does it only for the Hearing
Aid device.

Bug: 214245067
Test: phone call via BT -> switch to speaker-> close the call -> check
a2dp

Change-Id: If7c0120907029968669fa226aa7444bf86f834f5