Remove Expect from core library.

tests/standalone/io/http_head_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";
 
 void testHEAD(int totalConnections) {
   HttpServer server = new HttpServer();
   server.onError = (e) => Expect.fail("Unexpected error $e");
   server.listen("127.0.0.1", 0, backlog: totalConnections);
   server.addRequestHandler(
       (request) => request.path == "/test100",
       (HttpRequest request, HttpResponse response) {
         response.contentLength = 100;
@@ skipping 30 matching lines @@
           server.close();
         }
       };
     };
   }
 }
 
 void main() {
   testHEAD(4);
 }