audio_policy: remove low_latency

* This is causing issues where if you're in-call, and the screen
  locks, you'll end up with no sound in your call anymore. Also
  seems to happen when you receive a second call while already in
  call.

W/AudioTrack( 1111): AUDIO_OUTPUT_FLAG_FAST denied by client

Change-Id: I09d750f79d0e9ac7bc476443e5301dec79cce626