Makefile.libcompat: Tweak krb5 compat dirs

krb5/util contains both programs and libraries; trying to build that
for compat confuses bsd.prog.mk and results in unwanted files being
created in the source tree. Remove krb5/util and instead list only
the directories underneath krb5/util which contain libraries.

The libdata change from the diff isn't included; that will be fixed
in a different way.

Fixes: fb13ae28b2e8 ("Makefile.libcompat: Add krb5/util")
Reviewed by: ngie (previous version)
Differential Revision: https://reviews.freebsd.org/D51937