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 https://github.com/facebook/rocksdb/pull/3542
Differential Revision: D7088713
Pulled By: ajkr
fbshipit-source-id: 749ecafc6a9572f587f76e516547e07734349a54