Remove obsolete iptables-nftables support

"iptables over nftables tree (OBSOLETE, use iptables tree)"
(http://git.netfilter.org/iptables-nftables)

The latest iptables tree should have corrected nft integration now. This would require iptables git cbe036db892c298c33e77dec2c5129dbb4dccc2c or later (most likely the latest git master http://git.netfilter.org/iptables/log/)