Remove barback from the repo.

pkg/barback/test/barback_mode_test.dart

Index: pkg/barback/test/barback_mode_test.dart
diff --git a/pkg/barback/test/barback_mode_test.dart b/pkg/barback/test/barback_mode_test.dart
deleted file mode 100644
index 2d18f09933f50ddf366ea67271e00360cce50ea2..0000000000000000000000000000000000000000
--- a/pkg/barback/test/barback_mode_test.dart
+++ /dev/null
@@ -1,20 +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.
-
-library barback.test.barback_mode_test;
-
-import 'package:barback/barback.dart';
-import 'package:unittest/unittest.dart';
-
-import 'utils.dart';
-
-main() {
-  initConfig();
-  test("constructor uses canonical instances for DEBUG and RELEASE", () {
-    expect(identical(BarbackMode.DEBUG,
-        new BarbackMode(BarbackMode.DEBUG.name)), isTrue);
-    expect(identical(BarbackMode.RELEASE,
-        new BarbackMode(BarbackMode.RELEASE.name)), isTrue);
-  });
-}