Remove Expect from core library.

tests/standalone/io/http_server_early_server_close_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:async";
 import "dart:io";
 import "dart:isolate";
 
 class Server {
   Server() {
     HttpServer server = new HttpServer();
     server.listen("127.0.0.1", 0);
     port = server.port;
     server.defaultRequestHandler =
@@ skipping 21 matching lines @@
     c.onError = (e) {
       r.close();
     };
   }
 }
 
 main() {
   Server server = new Server();
   new Client(server.port);
 }