MediaPlayer: remove obsolete function setPlaybackRate from comments.
MediaPlayer: remove obsolete function setPlaybackRate from comments.

Bug: 24260668
Change-Id: I20733e52dbd2dab5eb10b4607a1c1aadb93a1332
(cherry picked from commit cd860ac06ca7a46e9638dd741ba731f066705eb5)

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base