move delete_file and remove_sourcemap_comment transformers to code_transformers

pkg/code_transformers/lib/src/remove_sourcemap_comment.dart

 // 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.
 
 /// Transformer that removes any sourcemap comments from javascript files.
-library web_components.src.remove_sourcemap_comment;
+library code_transformers.src.remove_sourcemap_comment;
 
 import 'dart:async';
 import 'package:barback/barback.dart';
 
 /// Transformer that removes any sourcemap comments from javascript files.
 /// Comments should be on their own line in the form: //# sourceMappingURL=*.map
 class RemoveSourcemapComment extends Transformer {
   BarbackSettings settings;
 
   RemoveSourcemapComment.asPlugin(this.settings);
 
   /// Only apply to files in release mode.
   isPrimary(_) => settings.mode == BarbackMode.RELEASE;
 
   apply(Transform transform) {
     var id = transform.primaryInput.id;
     return transform.readInputAsString(id).then((file) {
       if (file.contains(_SOURCE_MAP_COMMENT)) {
         transform.addOutput(new Asset.fromString(
             id, file.replaceAll(_SOURCE_MAP_COMMENT, '')));
       }
     });
   }
 }
 
 final RegExp _SOURCE_MAP_COMMENT = new RegExp(r'\n\s*\/\/# sourceMappingURL.*');