libvirt.spec.in: Don't distribute libvirtd.upstart
    
    Firstly, for rpm we are building libvirt with
    --init-script=systemd or --init-script=redhat. So upstart is
    never enabled. And only due to a bug we installed
    libvirtd.upstart file.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
    Reviewed-by: Pavel Hrdina <phrdina@redhat.com>