Add all-channel AudioTrack::setVolume() API

Add combined channel APIs setVolume to AudioTrack,
and remove obsolete getVolume.

Change-Id: I0c87bfdbff4f4292259fa33e65f67badbafd270b
diff --git a/media/libmedia/ToneGenerator.cpp b/media/libmedia/ToneGenerator.cpp
index 253602d..42584fe 100644
--- a/media/libmedia/ToneGenerator.cpp
+++ b/media/libmedia/ToneGenerator.cpp
@@ -1036,7 +1036,7 @@
         goto initAudioTrack_exit;
     }
 
-    mpAudioTrack->setVolume(mVolume, mVolume);
+    mpAudioTrack->setVolume(mVolume);
 
     mState = TONE_INIT;