dart:io | Revert addition of Link class, because it conflicts with a Link class in dart2js.

runtime/bin/file_patch.dart

 // Copyright (c) 2012, 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.
 
 patch class _FileUtils {
   /* patch */ static SendPort _newServicePort() native "File_NewServicePort";
 }
 
 patch class _File {
   /* patch */ static _exists(String path) native "File_Exists";
   /* patch */ static _create(String path) native "File_Create";
-  /* patch */ static _createLink(String path, String target)
-      native "File_CreateLink";
   /* patch */ static _delete(String path) native "File_Delete";
   /* patch */ static _directory(String path) native "File_Directory";
   /* patch */ static _lengthFromPath(String path) native "File_LengthFromPath";
   /* patch */ static _lastModified(String path) native "File_LastModified";
   /* patch */ static _open(String path, int mode) native "File_Open";
   /* patch */ static int _openStdio(int fd) native "File_OpenStdio";
   /* patch */ static _fullPath(String path) native "File_FullPath";
 }
 
 patch class _RandomAccessFile {
   /* patch */ static int _close(int id) native "File_Close";
   /* patch */ static _readByte(int id) native "File_ReadByte";
   /* patch */ static _read(int id, int bytes) native "File_Read";
   /* patch */ static _readList(int id, List<int> buffer, int offset, int bytes)
       native "File_ReadList";
   /* patch */ static _writeByte(int id, int value) native "File_WriteByte";
   /* patch */ static _writeList(int id, List<int> buffer, int offset, int bytes)
       native "File_WriteList";
   /* patch */ static _position(int id) native "File_Position";
   /* patch */ static _setPosition(int id, int position)
       native "File_SetPosition";
   /* patch */ static _truncate(int id, int length) native "File_Truncate";
   /* patch */ static _length(int id) native "File_Length";
   /* patch */ static _flush(int id) native "File_Flush";
 }
 
 List<int> _makeUint8ListView(List<int> source, int from, int to) {
   return new Uint8List.view(source.asByteArray(), from, to);
 }