graphics/vkd3d: drop FreeBSD < 12.2 workaround after 620968a43a5f
https://cgit.freebsd.org/src/commit/?id=92bcf7444cf5
https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/ab5dc9aceb34
https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/dcaf745f3ae
NetBSD and OpenBSD support is out of scope.