Fix not fallback to LE Audio when HFP removed active device

If the device connects to an LE audio device and HFP device, when the HFP
active device is set to null, the ActvieDeviceManager should try to
fallback to the LE Audio device.

Bug: 359743806
Test: atest BluetoothInstrumentationTests
Flag: Exempt, trivial and obvious fix.
Change-Id: I7e42f9788ee53914fd010b09b745ae37c4921db5