nftables is available since kernel 3.13 (released on 19 January 2014).
Major distributions have already provided nftables, and marked/called
iptables as deprecated or legacy.
Moreover, currently, iptables/libiptc backend does not support IPv6.
Hence, it is not necessary to keep iptables/libiptc backend anymore.
Let's drop it in the next release.
Note, fedora/centos have already disabled iptables/libiptc support since v249.
* The meson option '-Dintegration-tests=' has been deprecated, and will
be removed in a future release.
+ * The legacy iptables support through libiptc will be removed in v259.
+ Only nftables backend will be supported by systemd-networkd and
+ systemd-nspawn since v259.
+
Service manager/PID1:
* The PrivateUsers= unit setting now accepts a new value "full", which