AudioTrack: offload is not tied to USAGE_MEDIA

Offload support check now supports passing AudioAttributes.
Do not require AudioTrack usage to be USAGE_MEDIA, check of use
  case will be done in AudioSystem.isOffloadSupported().

Bug: 129133576
Test: use offload for USAGE_ASSISTANT
Change-Id: I00065fb936600cfcdf29bc019173699db7ec5a2f