Remove HttpClientRequest.response, as it's identical to HttpClientRequest.done.

tests/standalone/io/http_headers_state_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:isolate";
 import "dart:io";
 
 void test(int totalConnections, [String body]) {
@@ skipping 35 matching lines @@
             request.write(body);
             // Cannot mutate request headers when data has been sent.
             Expect.throws(
                 () => request.headers.add("X-Request-Header", "value2"),
                 (e) => e is HttpException);
           }
           request.close();
           // Cannot mutate request headers when data has been sent.
           Expect.throws(() => request.headers.add("X-Request-Header", "value3"),
                         (e) => e is HttpException);
-          return request.response;
+          return request.done;
         })
         .then((HttpClientResponse response) {
           // Cannot mutate response headers.
           Expect.throws(
               () => response.headers.add("X-Response-Header", "value"),
               (e) => e is HttpException);
           Expect.equals("value", response.headers.value("X-Response-Header"));
           response.listen((_) {}, onDone: () {
             // Do not close the connections before we have read the
             // full response bodies for all connections.
             if (++count == totalConnections) {
               client.close();
               server.close();
             }
           });
         });
     }
 
   });
 }
 
 void main() {
   test(5);
   test(5, "Hello and goodbye");
 }