remove pkg/mock

pkg/mock/lib/src/responder.dart

-// Copyright (c) 2014, 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.
-
-library mock.responder;
-
-import 'action.dart';
-
-/**
- * The behavior of a method call in the mock library is specified
- * with [Responder]s. A [Responder] has a [value] to throw
- * or return (depending on the type of [action]),
- * and can either be one-shot, multi-shot, or infinitely repeating,
- * depending on the value of [count (1, greater than 1, or 0 respectively).
- */
-class Responder {
-  final Object value;
-  final Action action;
-  int count;
-  Responder(this.value, [this.count = 1, this.action = Action.RETURN]);
-}