Fix a memory leak in WindowsThread

Summary:
_endthreadex does not return and thus objects
  for stack destructors do not run. This creates a memory leak.
  We remove the calls since _enthreadex called automatically after the
  threadproc returns i.e. thread exits.
Closes #3542

Differential Revision: D7088713

Pulled By: ajkr

fbshipit-source-id: 749ecafc6a9572f587f76e516547e07734349a54

port/win/win_thread.cc

@@ -166,7 +166,6 @@ unsigned int __stdcall  WindowsThread::Data::ThreadProc(void* arg) {
   auto ptr = reinterpret_cast<std::shared_ptr<Data>*>(arg);
   std::unique_ptr<std::shared_ptr<Data>> data(ptr);
   (*data)->func_();
-  _endthreadex(0);
   return 0;
 }
 } // namespace port