Remove barback from the repo.

pkg/barback/test/transformer/lazy_assets.dart

Index: pkg/barback/test/transformer/lazy_assets.dart
diff --git a/pkg/barback/test/transformer/lazy_assets.dart b/pkg/barback/test/transformer/lazy_assets.dart
deleted file mode 100644
index 5fa81d0b46bac6d5bc8955be3887bebf46cce2a1..0000000000000000000000000000000000000000
--- a/pkg/barback/test/transformer/lazy_assets.dart
+++ /dev/null
@@ -1,17 +0,0 @@
-// 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 barback.test.transformer.lazy_assets;
-
-import 'package:barback/barback.dart';
-
-import 'declare_assets.dart';
-
-/// Like [DeclareAssetsTransformer], but lazy.
-class LazyAssetsTransformer extends DeclareAssetsTransformer
-    implements LazyTransformer {
-  LazyAssetsTransformer(Iterable<String> declared, {Iterable<String> emitted,
-        String input})
-      : super(declared, emitted: emitted, input: input);
-}