Fix playback in variable speed audio.

- Recent changes to system/media broke variable speed playback.
- Traced to http://go/android-cl/132098 which presumed that variable
  speed playback wasn't using the renamed sample rate field, but we
  had our own copy of the field (it wasn't previously available in the
  api).
- This cl also fixes the TODO by removing our own copy of the fields,
  and using instead the defines from the OpenSL android api directly.

Bug: 5282965
Change-Id: I58033e9299d26d6a05259e4d50708d27fc3fa7e1