update to 2.4.5 (#1394902, #1476553)
    
    use upstream systemd unit
    include additional docs
    fix SELinux policy installation scriptlet logic (#1438190)
    drop HLL policy, CIL import is supported in 2.4+ and RHEL 7.3 ships 2.5
    add gcc to BRs, use set_build_flags macro
    add more missing SELinux rules
    silence last module removal semodule warning
    move upstream GPG key from look-aside cache to git repo