Make the Dart application library code stop using the "wrong way" service provider (a.k.a. exposed_…

mojo/dart/apptests/test_apps/pingpong_target/lib/main.dart

Index: mojo/dart/apptests/test_apps/pingpong_target/lib/main.dart
diff --git a/mojo/dart/apptests/test_apps/pingpong_target/lib/main.dart b/mojo/dart/apptests/test_apps/pingpong_target/lib/main.dart
index 8cceaa7954080d9018dade33132f3924c88f695f..5c619ef230c17d7ee0f44cc0d9ac04ad27c3f786 100644
--- a/mojo/dart/apptests/test_apps/pingpong_target/lib/main.dart
+++ b/mojo/dart/apptests/test_apps/pingpong_target/lib/main.dart
@@ -56,9 +56,6 @@ class PingPongApplication extends Application {
     // Provide the service implemented by PingPongServiceImpl.
     connection.provideService(PingPongService.serviceName,
         (endpoint) => new PingPongServiceImpl(this, endpoint));
-
-    // No services are required from the remote end.
-    connection.remoteServiceProvider.close();
   }
 
   Future closeApplication() async {