Remove Expect from core library.

tests/standalone/io/http_server_response_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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
+import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:scalarlist";
 
 void testServerRequest(void handler(server, request), {int bytes}) {
   HttpServer.bind().then((server) {
     server.listen((request) {
       handler(server, request);
     });
 
@@ skipping 111 matching lines @@
     }, test: (e) => e is HttpException);
   });
 }
 
 void main() {
   testResponseDone();
   testResponseAddStream();
   testBadResponseAdd();
   testBadResponseClose();
 }