NaCl: Cleanup: Remove PpapiPluginRegisterDefaultThreadCreator()

ppapi/native_client/src/shared/ppapi_proxy/nacl.scons

 # -*- python -*-
 # 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.
 
 Import('env')
 
 # Underlay $SOURCE_ROOT/gpu in this directory.
 Dir('.').addRepository(Dir('#/../gpu'))
 
@@ skipping 86 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'] + command_buffer_srcs,
     LIBS=['pthread',
          'srpc',
          'gio',
          'platform',
         ])
 
 header_install = env.AddHeaderToSdk(['ppruntime.h'])
 env.AddLibraryToSdk(libppruntime)
 
 # Clients that overload main() will use ppruntime.h.
 env.Requires(libppruntime, header_install)