kerberos5: Fix the Heimdal pkgbase build

When LIB_PACKAGE was added, MIT Kerberos was updated to use it but
Heimdal was not, so it still used PACKAGE=kerberos-lib. Since we
deleted kerberos-lib-all.ucl, this caused update-packages to fail
when WITHOUT_MITKRB5 is set.

Change the Heimdal libraries to use LIB_PACKAGE by setting this in
kerberos5/lib/Makefile.inc, and remove PACKAGE=kerberos-lib from the
individual Makefiles for each library. This means Heimdal gets the
same set of packages as MIT Kerberos, except for kerberos-kdc which
we don't create for Heimdal.

Fixes: 929f5966a9fd ("packages: Improve handling of -lib packages")
Reported by: jlduran
Reviewed by: jlduran, cy
Differential Revision: https://reviews.freebsd.org/D52371