NaCl: Address some TODOs from moving PPAPI IRT interface into the Chromium repo

ppapi/nacl_irt/irt_ppapi.h

 /*
  * Copyright 2014 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_NACL_IRT_IRT_PPAPI_H_
 #define PPAPI_NACL_IRT_IRT_PPAPI_H_
 
 #include <stddef.h>
@@ skipping 15 matching lines @@
    * We use uintptr_t as the thread ID type because pthread_t is not
    * part of the stable ABI; a user thread library might choose an
    * arbitrary size for its own pthread_t.
    */
   int (*thread_create)(uintptr_t* tid,
                        void (*func)(void* thread_argument),
                        void* thread_argument);
   int (*thread_join)(uintptr_t tid);
 };
 
-/*
- * TODO(mseaborn): Make this unconditional after the definition of the
- * struct has been removed from the NaCl side's irt.h.
- */
-#if !defined(NACL_IRT_PPAPIHOOK_v0_1)
-
 #define NACL_IRT_PPAPIHOOK_v0_1 "nacl-irt-ppapihook-0.1"
 struct nacl_irt_ppapihook {
   int (*ppapi_start)(const struct PP_StartFunctions*);
   void (*ppapi_register_thread_creator)(const struct PP_ThreadFunctions*);
 };
 
 #endif
-
-#endif