[HA Audio Output] When switching between paired hearing aids and LE-audio, it...

[HA Audio Output] When switching between paired hearing aids and LE-audio, it will call removePreferredDevicesForStrategy

Root Cause: Since the audio routing feature is not ready, it should not
run the code at this moment.

Solution: Hide the audio routing related code behind the feature flag

Bug: 303001133
Test: atest HearingAidDeviceManagerTest
Change-Id: I3e795d2d5175752144e783e09764c763c0e4ee4b