Remove barback from the repo.

pkg/barback/test/transformer/create_asset.dart

Index: pkg/barback/test/transformer/create_asset.dart
diff --git a/pkg/barback/test/transformer/create_asset.dart b/pkg/barback/test/transformer/create_asset.dart
deleted file mode 100644
index 82e80b37d4ba8a3e681ae5066126aa5482800c6d..0000000000000000000000000000000000000000
--- a/pkg/barback/test/transformer/create_asset.dart
+++ /dev/null
@@ -1,23 +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.transformer.create_asset;
-
-import 'package:barback/barback.dart';
-
-import 'mock.dart';
-
-/// A transformer that outputs an asset with the given id.
-class CreateAssetTransformer extends MockTransformer {
-  final String output;
-
-  CreateAssetTransformer(this.output);
-
-  bool doIsPrimary(AssetId id) => true;
-
-  void doApply(Transform transform) {
-    transform.addOutput(
-        new Asset.fromString(new AssetId.parse(output), output));
-  }
-}