BT: HFP: Remove redundant unbindings to HeadsetService

When onServiceDisconnected gets called, no need to
call doUnbind() for HeadsetService as unbinding to
HeadsetService is taken care by BluetoothManagerService.
This fixes deadlock during BT turn off where BluetoothHeadset's
doUnbind() is called as part of BT state change callback
processing and BluetoothHeadset's onServiceDisconnected.

In BluetoothManagerService, remove unbind attempt while
removing proxy as unbind to HeadsetService is already
done from unbindBluetoothProfileService().

CRs-Fixed: 2488256
Change-Id: I0f86a9fbe02dfaf586a0a9bfe1c351e1298d063b