Fix systemd dependency
    
    systemd is used during the build only to get systemunitdir from
    systemd.pc. That pkgconfig file is now part of systemd, and
    systemd-devel does not provide that, even indirectly.  While beakerlib
    ends up pulling in systemd, that should not be relied upon, and does not
    help for RHEL/ELN where beakerlib is now disabled.