Remove Expect from core library.

tests/standalone/io/http_server_test.dart

 // Copyright (c) 2013, 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;
   HttpServer server;
 
   void test(void onDone()) {
 
     Expect.equals(socket.port, server.port);
@@ skipping 38 matching lines @@
         Expect.throws(() => server.port);
         socket.close();
       });
     });
   });
 }
 
 void main() {
   testListenOn();
 }