Clear listeners when adding a new one in AudioDeviceVolumeManager

Currently, multiple absolute volume listeners from the same controller
can be notified of volume change events because old ones are not removed
from AudioDeviceVolumeManager.

This CL removes existing listeners for a device when a new one is added.
We also no longer forbid re-adding a listener currently in
AudioDeviceVolumeManager's list, as it might have been removed from
AudioService.

Bug: 231433390
Test: manual; atest android.hdmicec.cts.playback.HdmiCecAvcToTvTest
Change-Id: If7ecd58880001b955565e0f65ede9f0787e1be49