Remove Expect from core library.

tests/standalone/io/http_shutdown_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";
 
 void test1(int totalConnections) {
   // Server which just closes immediately.
   HttpServer.bind().then((server) {
     server.listen((HttpRequest request) {
       request.response.close();
     });
 
@@ skipping 177 matching lines @@
   test1(10);
   test2(1, 10);
   test2(10, 10);
   test2(10, 1000);
   test3(1);
   test3(10);
   test4();
   test5(1);
   test5(10);
 }