nft: revert compat expressions in userdata

nft: revert compat expressions in userdata

This reverts the following commits:

758cfe51968a ("configure: Auto-detect libz unless explicitly requested")
fdb541cddad0 ("tests: iptables-test: Add nft-compat variant")
7746fa0b1619 ("nft: Embed compat extensions in rule userdata")
ff5f6a208efc ("nft-ruleparse: Fallback to compat expressions in userdata")
f6f0f4f55794 ("nft: Introduce UDATA_TYPE_COMPAT_EXT")

The main intended user for '--compat' will likely go away. It is also
unlikely the 'iptables-only-emits-native-nft' will ever come to pass.

If there is ever a demand of iptables-to-native-nft that can list rules
even if decompilation step fails then we can always resurrect this again
if needed be.

Signed-off-by: Florian Westphal <fw@strlen.de>