Update OLD_DIRS for various targets so that some of the branches of
directories are pruned when the appropriate knobs are turned.

Specifically, turning off bsdconfig, locales, examples, i18n, man,
ntp, syscons. It may not seem like a lot, but it helps when trying
to keep an x86 image under 96MB for MFSRoot netbooting.

Reviewed by: ngie
Differential Revision: https://reviews.freebsd.org/D9558