c11/threads.h, remove _SIMPLE_MTX_INITIALIZER_NP as it's temporary non-standard hack to ease transition

// FIXME: temporary non-standard hack to ease transition
#  define _MTX_INITIALIZER_NP {(void*)-1, -1, 0, 0, 0, 0}
#  define ONCE_FLAG_INIT {0}
#  define TSS_DTOR_ITERATIONS 1
#elif defined(HAVE_PTHREAD)
typedef pthread_cond_t  cnd_t;
typedef pthread_t       thrd_t;
typedef pthread_key_t   tss_t;
typedef pthread_mutex_t mtx_t;
typedef pthread_once_t  once_flag;
// FIXME: temporary non-standard hack to ease transition
#  define _MTX_INITIALIZER_NP PTHREAD_MUTEX_INITIALIZER
#  define ONCE_FLAG_INIT PTHREAD_ONCE_INIT
#  ifdef INIT_ONCE_STATIC_INIT
#    define TSS_DTOR_ITERATIONS PTHREAD_DESTRUCTOR_ITERATIONS
#  else
#    define TSS_DTOR_ITERATIONS 1  // assume TSS dtor MAY be called at least once.
#  endif
#else
#  error Not supported on this platform.
#endif