Remove apparently unused field

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=173871144

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaPeriod.java

@@ -64,7 +64,6 @@ import java.util.List;
   private CompositeSequenceableLoader sequenceableLoader;
   private DashManifest manifest;
   private int periodIndex;
-  private List<AdaptationSet> adaptationSets;
 
   public DashMediaPeriod(int id, DashManifest manifest, int periodIndex,
       DashChunkSource.Factory chunkSourceFactory,  int minLoadableRetryCount,
@@ -81,8 +80,8 @@ import java.util.List;
     this.allocator = allocator;
     sampleStreams = newSampleStreamArray(0);
     sequenceableLoader = new CompositeSequenceableLoader(sampleStreams);
-    adaptationSets = manifest.getPeriod(periodIndex).adaptationSets;
-    Pair<TrackGroupArray, TrackGroupInfo[]> result = buildTrackGroups(adaptationSets);
+    Pair<TrackGroupArray, TrackGroupInfo[]> result =
+        buildTrackGroups(manifest.getPeriod(periodIndex).adaptationSets);
     trackGroups = result.first;
     trackGroupInfos = result.second;
   }
@@ -90,7 +89,6 @@ import java.util.List;
   public void updateManifest(DashManifest manifest, int periodIndex) {
     this.manifest = manifest;
     this.periodIndex = periodIndex;
-    adaptationSets = manifest.getPeriod(periodIndex).adaptationSets;
     if (sampleStreams != null) {
       for (ChunkSampleStream<DashChunkSource> sampleStream : sampleStreams) {
         sampleStream.getChunkSource().updateManifest(manifest, periodIndex);