Remove barback from the repo.

pkg/barback/test/transformer/lazy_rewrite.dart

Index: pkg/barback/test/transformer/lazy_rewrite.dart
diff --git a/pkg/barback/test/transformer/lazy_rewrite.dart b/pkg/barback/test/transformer/lazy_rewrite.dart
deleted file mode 100644
index 63bffb607a1ff6f456fb0ce5149180b049a15fbf..0000000000000000000000000000000000000000
--- a/pkg/barback/test/transformer/lazy_rewrite.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_rewrite;
-
-import 'package:barback/barback.dart';
-
-import 'declaring_rewrite.dart';
-
-/// Like [RewriteTransformer], but returns a lazy asset that doesn't perform the
-/// rewrite until it's materialized.
-class LazyRewriteTransformer extends DeclaringRewriteTransformer
-    implements LazyTransformer {
-  LazyRewriteTransformer(String from, String to)
-      : super(from, to);
-}