Cleanup: remove package "analyzer2dart".

pkg/analyzer2dart/test/output_helper.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.
-
-/// Helper classes for testing compiler output.
-library test.output_helper;
-
-import 'dart:async';
-
-
-class CollectingOutputProvider {
-  StringBufferSink output;
-
-  EventSink<String> call(String name, String extension) {
-    return output = new StringBufferSink();
-  }
-}
-
-class StringBufferSink implements EventSink<String> {
-  StringBuffer sb = new StringBuffer();
-
-  void add(String text) {
-    sb.write(text);
-  }
-
-  void addError(errorEvent, [StackTrace stackTrace]) {}
-
-  void close() {}
-
-  String get text => sb.toString();
-}
-