pf: remove unused ioctls.

Several ioctls are unused in pf, in the sense that no base utility
references them. Additionally, a cursory review of pf-based ports
indicates they're not used elsewhere either. Some of them have been
unused since the original import. As far as I can tell, they're also
unused in OpenBSD. Finally, removing this code removes the need for
future pf work to take them into account.

Reviewed by: kp
Differential Revision: https://reviews.freebsd.org/D16076