nptl: Move mtx_init into libc

nptl: Move mtx_init into libc

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

The calls to __pthread_mutex_init, __pthread_mutexattr_init,
__pthread_mutexattr_settype are now private and no longer need
to be exported.  This allows the removal of the newly added
GLIBC_2.34 symbol versions for those functions.

Also clean up some weak declarations in <libc-lockP.h> for
these functions.  They are not needed and potentially incorrect
for static linking of mtx_init.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>