s390: Remove _dl_skip_args usage

Since ad43cac4 the generic code already shuffles the argv/envp/auxv
on the stack to remove the ld.so own arguments and thus _dl_skip_args
is always 0.   So there is no need to adjust the argc or argv.

Checked on s390x-linux-gnu and s390-linux-gnu.

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