Removed obsolete code

utils/lib/file_system_memory.dart

-// Copyright (c) 2011, 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.
-
-// TODO(terry): Investigate common library for file I/O shared between frog and tools.
-
-library file_system_memory;
-
-import 'file_system.dart';
-
-/**
- * [FileSystem] implementation a memory buffer.
- */
-class MemoryFileSystem implements FileSystem {
-  StringBuffer buffer;
-
-  MemoryFileSystem() : this.buffer = new StringBuffer();
-
-  void writeString(String outfile, String text) {
-    buffer.write(text);
-  }
-
-  String readAll(String filename) {
-    return buffer.toString();
-  }
-
-  bool fileExists(String filename) {
-    return true;
-  }
-
-  void createDirectory(String path, [bool recursive]) {
-    // TODO(terry): To be implement.
-    throw 'createDirectory() is not implemented by MemoryFileSystem yet.';
-  }
-
-  void removeDirectory(String path, [bool recursive]) {
-    // TODO(terry): To be implement.
-    throw 'removeDirectory() is not implemented by MemoryFileSystem yet.';
-  }
-}