Bootstrap: Prune building from pre-FreeBSD 11 support

We don't need to bootstrap lex or md4 anymore.
Cat doesn't need to be bootstrapped (but is needed for buildkernel)
cruncgen doesn't need to be bootstrapped at all.
kbdcontrol isn't needed

Sponsored by: Netflix
Pull Request: https://github.com/freebsd/freebsd-src/pull/554