Revert "Import org.junit.Assert instead of junit.framework.Assert."

This reverts commit a88470964c.

It broke Android builds:
app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java:46: error: package org.junit does not exist
import static org.junit.Assert.*;
                       ^
TBR=glaznev@webrtc.org,pthatcher@webrtc.org
BUG=none

Review URL: https://webrtc-codereview.appspot.com/52039004

Cr-Commit-Position: refs/heads/master@{#9357}

talk/app/webrtc/java/testcommon/src/org/webrtc/PeerConnectionTest.java

@@ -43,7 +43,7 @@ import java.util.TreeSet;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
-import static org.junit.Assert.*;
+import static junit.framework.Assert.*;
 
 /** End-to-end tests for PeerConnection.java. */
 public class PeerConnectionTest {