ActiveDeviceManager: Fix A2DP or HFP Active device changes to null

When A2DP or HFP devices is removed from the Active Devices, it shall
not inactivate LeAudioDevice when not needed.

This is regression after:
7cdf85a0 Updates active device policy to support dual mode audio

Note: HFP case there is similar logic which also was fixed

Bug: 367917846
Flag: Exempt, Obvious fix, regression tested with unit tests
Test: atest ActiveDeviceManagerTest
Change-Id: I6bb71abb746e68ec9a833f0756e4a3109bd101db