Documentation: Remove :manpage: from non-existing man pages

Documentation: Remove :manpage: from non-existing man pages

Removing :manpage: from non-existing man pages (xyzzy(2), xyzzyat(2),
fxyzzy(3) in adding-syscalls.rst, including translations) prevent
adding link to nonexisting man pages when using manpages_url in next
commit.

While at it, add also missing '(2)' in sp_SP translation.

Reviewed-by: Alejandro Colomar <alx@kernel.org>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260113113612.315748-2-pvorel@suse.cz>