bpo-30832: Remove own implementation for thread-local storage (#2537)

* bpo-30832: Remove own implementation for thread-local storage

CPython has provided the own implementation for thread-local storage
(TLS) on Python/thread.c, it's used in the case which a platform has
not supplied native TLS.  However, currently all supported platforms
(NT and pthreads) have provided native TLS and defined the
Py_HAVE_NATIVE_TLS macro with unconditional in any case.

* bpo-30832: replace NT with Windows

* bpo-30832: change to directive chain

* bpo-30832: remove comemnt which making no sense