OptionalObsoleteFiles: Update Kerberos entries

Consolidate the various lists of Kerberos files into three sets:
common files, files only installed by MIT Kerberos, and files only
installed by Heimdal. This avoids having to list the same files in
multiple places and makes the logic a lot easier to maintain.

The new file lists were created by comparing the actual result of
make installworld with the various options enabled or disabled.

Reviewed by: des, cy
Differential Revision: https://reviews.freebsd.org/D51874