Remove Expect from core library.

tests/standalone/io/http_server_test.dart

 // Copyright (c) 2012, 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.
 
+import "package:expect/expect.dart";
 import "dart:io";
 import "dart:isolate";
 
 void testListenOn() {
   ServerSocket socket = new ServerSocket("127.0.0.1", 0, 5);
 
   socket.onError = (Exception e) {
     Expect.fail("ServerSocket closed unexpected");
   };
 
@@ skipping 41 matching lines @@
   test(() {
     test(() {
       socket.close();
     });
   });
 }
 
 void main() {
   testListenOn();
 }