iptables in nft mode now prints an error for non-existent chains
iptables in nft mode now prints an error for non-existent chains

This reverts part of "Add support for iptables in nftables mode.",
which was added to work around some temporary issues in unreleased
iptables versions that have since been corrected upstream.

This specific issue was fixed in:

03572549df349455fcade80dfab0b28904975330
xtables: Print error when listing non-existent chains

coreos/go-iptables,coreos/go-iptables