Revert "no need to explicitly list krb5-libs"
    
    Currently, krb5-libs is pulled in by various other packages that are
    already part of the fedora-toolbox OCI image. Unless someone is keeping
    a close eye on the contents of the image, a change in the package
    dependencies or the contents of the base fedora OCI image can cause
    krb5-libs to go missing from the fedora-toolbox image.
    
    This would be undesirable because toolbox(1) relies on the presence
    of the /etc/krb5.conf file and the /etc/krb5.conf.d directory to set
    up Kerberos inside a toolbox container, and those are provided by the
    krb5-libs package.
    
    Therefore, explicitly listing krb5-libs prevents us from accidentally
    losing Kerberos integration in toolbox containers, and doesn't cost us
    anything because it's already part of the image anyway.
    
    This reverts commit f552b51ec2ff429f1cb3da1a0eb8c61c6e57af95.