Release streams in fake adaptive media period.

Releasing the media period should also release the sample streams
to allow resources to be cleaned up.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=168201377

testutils/src/main/java/com/google/android/exoplayer2/testutil/FakeAdaptiveMediaPeriod.java

@@ -54,6 +54,14 @@ public class FakeAdaptiveMediaPeriod extends FakeMediaPeriod
   }
 
   @Override
+  public void release() {
+    super.release();
+    for (ChunkSampleStream<FakeChunkSource> sampleStream : sampleStreams) {
+      sampleStream.release();
+    }
+  }
+
+  @Override
   public void prepare(Callback callback, long positionUs) {
     super.prepare(callback, positionUs);
     this.callback = callback;