Fix: remove obsolete callback

MobileLibrary/Android/SampleApps/TunneledWebView/app/src/main/java/ca/psiphon/tunneledwebview/MainActivity.java

@@ -264,11 +264,6 @@ public class MainActivity extends AppCompatActivity
 
     }
 
-    @Override
-    public void onSplitTunnelRegion(String region) {
-        logMessage("split tunnel region: " + region);
-    }
-
     @Override
     public void onUntunneledAddress(String address) {
         logMessage("untunneled address: " + address);