Remove unnecessary cloning.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125454697

library/src/main/java/com/google/android/exoplayer/TrackSelection.java

@@ -57,7 +57,7 @@ public final class TrackSelection {
    * @return The index of the selected track.
    */
   public int getTrack(int index) {
-    return getTracks()[index];
+    return tracks[index];
   }
 
   /**