pkg/unittest: remove deprecated features

pkg/unittest/lib/matcher.dart

Index: pkg/unittest/lib/matcher.dart
diff --git a/pkg/unittest/lib/matcher.dart b/pkg/unittest/lib/matcher.dart
deleted file mode 100644
index 3fd692e13440419d1801a89bc8bff687c5936360..0000000000000000000000000000000000000000
--- a/pkg/unittest/lib/matcher.dart
+++ /dev/null
@@ -1,12 +0,0 @@
-// 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.
-
-/// `unittest.matcher` has been moved to the `matcher` package.
-///
-/// Add `matcher` to your `pubspec.yaml` file and import it via
-/// `import 'package:matcher/matcher.dart';`
-@deprecated
-library unittest.matcher;
-
-export 'package:matcher/matcher.dart';