NaCl: Cleanup: Remove PpapiPluginRegisterDefaultThreadCreator()

ppapi/native_client/src/shared/ppapi_proxy/ppapi_proxy_untrusted.gyp

 # Copyright (c) 2012 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.
 
 {
   'includes': [
     '../../../../../native_client/build/common.gypi',
   ],
   'targets': [
     {
@@ skipping 83 matching lines @@
           'plugin_ppp_messaging_rpc_server.cc',
           'plugin_ppp_mouse_lock_rpc_server.cc',
           'plugin_ppp_printing_rpc_server.cc',
           'plugin_ppp_scrollbar_rpc_server.cc',
           'plugin_ppp_selection_rpc_server.cc',
           'plugin_ppp_widget_rpc_server.cc',
           'plugin_ppp_zoom_rpc_server.cc',
           'plugin_ppp_rpc_server.cc',
           'plugin_resource.cc',
           'plugin_resource_tracker.cc',
-          'plugin_threading.cc',
           'plugin_upcall.cc',
           'ppp_instance_combined.cc',
           'proxy_var.cc',
           'proxy_var_cache.cc',
           'utility.cc',
           'view_data.cc',
           # Autogenerated files
           'ppp_rpc_server.cc',
           'ppb_rpc_client.cc',
           'upcall_client.cc'
         ],
       },
     },
   ],
 }