nptl: Move call_once into libc

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

This change also turns __pthread_once into a compatibility symbol
because after the call_once move, an internal call to __pthread_once
can be used.  This an adjustment to __libc_once: Outside libc (e.g.,
in nscd), it has to call pthread_once.  With __pthread_once as a
compatibility symbol, it is no longer to add a new GLIBC_2.34
version after the move from libpthread, and this commit removes
the new __pthread_once@@GLIBC_2.34 version.

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