remove pkg/mock

pkg/mock/test/mock_regexp_negative_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.
-
-library mock.mock_regexp_negative_test;
-
-import 'package:unittest/unittest.dart' show test;
-import 'package:matcher/matcher.dart';
-import 'package:mock/mock.dart';
-
-void main() {
-  test('Mocking: RegExp CallMatcher bad', () {
-    var m = new Mock();
-    m.when(callsTo(matches('^[A-Z]'))).
-           alwaysThrow('Method names must start with lower case.');
-    m.Test();
-  });
-}