Remove experimental ExternalSymbolCallback feature. This is not needed...

src/api.cc

 // Copyright 2007-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2702 matching lines @@
   i::Heap::SetGlobalGCPrologueCallback(callback);
 }
 
 
 void V8::SetGlobalGCEpilogueCallback(GCCallback callback) {
   if (IsDeadCheck("v8::V8::SetGlobalGCEpilogueCallback()")) return;
   i::Heap::SetGlobalGCEpilogueCallback(callback);
 }
 
 
-void V8::SetExternalSymbolCallback(ExternalSymbolCallback callback) {
-  if (IsDeadCheck("v8::V8::SetExternalSymbolCallback()")) return;
-  i::Heap::SetExternalSymbolCallback(callback);
-}
-
 void V8::PauseProfiler() {
 #ifdef ENABLE_LOGGING_AND_PROFILING
   i::Logger::PauseProfiler();
 #endif
 }
 
 void V8::ResumeProfiler() {
 #ifdef ENABLE_LOGGING_AND_PROFILING
   i::Logger::ResumeProfiler();
 #endif
@@ skipping 282 matching lines @@
       reinterpret_cast<HandleScopeImplementer*>(storage);
   List<void**>* blocks_of_archived_thread = thread_local->Blocks();
   v8::ImplementationUtilities::HandleScopeData* handle_data_of_archived_thread =
       &thread_local->handle_scope_data_;
   Iterate(v, blocks_of_archived_thread, handle_data_of_archived_thread);
 
   return storage + ArchiveSpacePerThread();
 }
 
 } }  // namespace v8::internal