Remove Expect from core library.

tests/lib/async/stream_controller_async_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Test the basic StreamController and StreamController.singleSubscription.
 library stream_controller_async_test;
 
+import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:isolate';
 import '../../../pkg/unittest/lib/unittest.dart';
 import 'event_helper.dart';
 
 testController() {
   // Test fold
   test("StreamController.fold", () {
     StreamController c = new StreamController.broadcast();
     Stream stream = c.stream;
@@ skipping 434 matching lines @@
   testFuture("fold", (s, act) => s.fold(0, (a,b) => act(b)));
 }
 
 main() {
   testController();
   testSingleController();
   testExtraMethods();
   testPause();
   testRethrow();
 }