Revert 87415 - Convert more interfaces to the new thunk system. This goes up to and including

ppapi/thunk/ppb_file_system_api.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef PPAPI_THUNK_PPB_FILE_SYSTEM_API_H_
-#define PPAPI_THUNK_PPB_FILE_SYSTEM_API_H_
-
-#include "ppapi/c/dev/ppb_file_system_dev.h"
-
-namespace ppapi {
-namespace thunk {
-
-class PPB_FileSystem_API {
- public:
-  virtual int32_t Open(int64_t expected_size,
-                       PP_CompletionCallback callback) = 0;
-  virtual PP_FileSystemType_Dev GetType() = 0;
-};
-
-}  // namespace thunk
-}  // namespace ppapi
-
-#endif  // PPAPI_THUNK_PPB_FILE_SYSTEM_API_H_