Avoid memory leaks by removing callbacks from surface when SimpleExoPlayer is released.

Without this developers which reuse a SurfaceHolder with multiple instances of
SimpleExoPlayer need to call simpleExoPlayer.setVideoSurfaceHolder(null) to get
the SimpleExoPlayer.ComponentListener removed from the surface holder. If they
don't, the component listener is still registered and as a member class leaks
an instance of simpleExoPlayer.

Issue #1855

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135292439

library/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java

@@ -456,6 +456,7 @@ public final class SimpleExoPlayer implements ExoPlayer {
   @Override
   public void release() {
     player.release();
+    removeSurfaceCallbacks();
   }
 
   @Override