This man-page is based on OpenBSD's securelevel(7), and the copyright was
not reflecting that (probably due to a copy/paste error on my part; I can't
remember).
Noticed by Jeremy C. Reed, thanks!
While it's true that it's part of the traditional 4.4BSD security model,
there may come a time where a different "primary" security model used for
fine-grained privileges (ie., splitting root's responsibilities to various
privileges that can be assigned) may want to still have a securelevel
setting.
Idea from Daniel Carosone:
http://mail-index.netbsd.org/tech-security/2006/08/25/0001.html
The location of the removed files, for reference, was:
src/secmodel/bsd44/secmodel_bsd44_securelevel.c
src/secmodel/bsd44/securelevel.h