Remove code conditional on S_SPLINT_S

Remove code conditional on S_SPLINT_S

I don't know for sure what that is, but it's redefining setlocale(3)
and LC_ALL, which is are defined by C99, so it's supect of being some
variety of an extinct dynosaur.  Maybe related to the Dodo.

Link: <https://github.com/shadow-maint/shadow/pull/600>
Cc: Christian Göttsche <cgzones@googlemail.com>
Cc: Iker Pedrosa <ipedrosa@redhat.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Alejandro Colomar <alx@kernel.org>