Deprecate LoopingMediaSource for indefinite looping

ExoPlayer.setRepeatMode should be preferred. Deprecate
the constructor and update the relevant documentation.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=157829207

library/core/src/main/java/com/google/android/exoplayer2/source/LoopingMediaSource.java

@@ -23,19 +23,21 @@ import com.google.android.exoplayer2.util.Assertions;
 import java.io.IOException;
 
 /**
- * Loops a {@link MediaSource}.
+ * Loops a {@link MediaSource} a specified number of times.
+ * <p>
+ * Note: To loop a {@link MediaSource} indefinitely, it is usually better to use
+ * {@link ExoPlayer#setRepeatMode(int)}.
  */
 public final class LoopingMediaSource implements MediaSource {
 
-  private static final String TAG = "LoopingMediaSource";
-
   private final MediaSource childSource;
   private final int loopCount;
 
   private int childPeriodCount;
 
   /**
-   * Loops the provided source indefinitely.
+   * Loops the provided source indefinitely. Note that it is usually better to use
+   * {@link ExoPlayer#setRepeatMode(int)}.
    *
    * @param childSource The {@link MediaSource} to loop.
    */