Revert "bpo-36084: Add native thread ID to threading.Thread objects (GH-11993)" (GH-13458)

This reverts commit 4959c33d25.

Python/thread_pthread.h

@@ -12,12 +12,6 @@
 #endif
 #include <signal.h>
 
-#if defined(__linux__)
-#include <sys/syscall.h>
-#elif defined(__FreeBSD__)
-#include <pthread_np.h>
-#endif
-
 /* The POSIX spec requires that use of pthread_attr_setstacksize
    be conditional on _POSIX_THREAD_ATTR_STACKSIZE being defined. */
 #ifdef _POSIX_THREAD_ATTR_STACKSIZE
@@ -308,27 +302,6 @@ PyThread_get_thread_ident(void)
     return (unsigned long) threadid;
 }
 
-unsigned long
-PyThread_get_thread_native_id(void)
-{
-    if (!initialized)
-        PyThread_init_thread();
-#ifdef __APPLE__
-    uint64_t native_id;
-    pthread_threadid_np(NULL, &native_id);
-#elif defined(__linux__)
-    pid_t native_id;
-    native_id = syscall(__NR_gettid);
-#elif defined(__FreeBSD__)
-    pid_t native_id;
-    native_id = pthread_getthreadid_np();
-#else
-    unsigned long native_id;
-    native_id = 0;
-#endif
-    return (unsigned long) native_id;
-}
-
 void _Py_NO_RETURN
 PyThread_exit_thread(void)
 {