Revert --compat option related commits

Revert --compat option related commits

This reverts the following commits:

b14c971db6db0 ("tests: Test compat mode")
11c464ed015b5 ("Add --compat option to *tables-nft and *-nft-restore commands")
ca709b5784c98 ("nft: Introduce and use bool nft_handle::compat")
402b9b3c07c81 ("nft: Pass nft_handle to add_{target,action}()")

This implementation of a compatibility mode implements rules using
xtables extensions if possible and thus relies upon existence of those
in kernel space. Assuming no viable replacement for the internal
mechanics of this mode will be found in foreseeable future, it will
effectively block attempts at deprecating and removing of these xtables
extensions in favor of nftables expressions and thus hinder upstream's
future plans for iptables.

Signed-off-by: Phil Sutter <phil@nwl.cc>