nptl: Move pthread_setattr_default_np into libc

The symbol was moved using scripts/move-symbol-to-libc.py.

The export of  __default_pthread_attr_freeres is temporary.  There
is a minor regression in freeres coverage because in the dynamic case,
__default_pthread_attr_freeres is no longer called if libpthread is
not linked in.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>