netfilter: remove unused parameters in nf_ct_l4proto_[un]register_sysctl()

These parameters aren't used now.
So remove them.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>