Removed options:
--enable-atomic - removed 9.13.3 (commit 5024)
--enable-fetchlimit - removed pre-bind9
--enable-ipv6 - made default 9.14
--enable-openssl-hash - removed 9.14, default was already yes
--enable-seccomp - removed 9.13.0 (commit 4898)
--enable-sit - removed 9.11, replaced with DNS COOKIE option in configs (commit 4152)
--enable-threads - on-threaded support removed 9.13.3 (commit 5011)
--with-ecdsa - comes from openssl availability (removed 9.14)
--with-eddsa - comes from openssl availability (removed 9.14)
--with-geoip - marked as obsolete in 9.16
--with-randomdev - removed 9.13.0 (commit 4936)
--without-gost - GOST support removed 9.13.1 (commit 4961)
There don't seem to be any new options added that seem like must-haves,
so unless someone speaks up I'm not going to be adding anything right
now.