Remove WITHOUT_{CAPSICUM,CASPER} options

At this point CAPSICUM and CASPER are merely forced on via the newly
added __REQUIRED_OPTIONS list; after stable/14 branches I'll sweep
the tree for MK_{CAPSICUM,CASPER}.

This change will not be MFCed.

Discussed on: freebsd-arch
Differential Revision: https://reviews.freebsd.org/D40592