branches: 1.1.2; 1.1.4; 1.1.8; 1.1.16; 1.1.18;
Make securelevel a "secmodel" of its own.

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