Stop ignoring media key events in PhoneFallbackEventHandler while in call

Without the extra check, keys  will be routed to the telecom service via
MediaSessionService. The telecom service can decide the media key handling.

Bug: 187527519
Test: Manually press media play/pause key on 3.5mm headset while in call with Pixel 3a
Change-Id: I01002a83e0b752f8355dca307b42400a9489097a