Update the demo app to use the stable ExoPlayer.Builder constructor

The ExoPlayer.Builder constructor overloads are only needed for apps
trying to ensure certain classes are removed by R8/proguard, which isn't
relevant for the demo app.

PiperOrigin-RevId: 407819694

demos/main/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java

@@ -269,7 +269,8 @@ public class PlayerActivity extends AppCompatActivity
       trackSelector = new DefaultTrackSelector(/* context= */ this);
       lastSeenTracksInfo = TracksInfo.EMPTY;
       player =
-          new ExoPlayer.Builder(/* context= */ this, renderersFactory)
+          new ExoPlayer.Builder(/* context= */ this)
+              .setRenderersFactory(renderersFactory)
               .setMediaSourceFactory(mediaSourceFactory)
               .setTrackSelector(trackSelector)
               .build();