Android: Fix memory leak for remote MediaStream

BUG=webrtc:4892
R=glaznev@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1308733004 .

Cr-Commit-Position: refs/heads/master@{#9797}

webrtc/examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java

@@ -911,11 +911,7 @@ public class PeerConnectionClient {
       executor.execute(new Runnable() {
         @Override
         public void run() {
-          if (peerConnection == null || isError) {
-            return;
-          }
           remoteVideoTrack = null;
-          stream.videoTracks.get(0).dispose();
         }
       });
     }