There is no 'udev.target' unit in systemd (only 'udev.service')
yet libvirtd's unit file had a dep on one. There's no compelling
reason for a dep on udev, so remove it altogether.
Reported-by: Avi Kivity <avi@redhat.com>
(cherry picked from commit 6cfc3f8f4facc7f549ee494b216bde18d15a1d33)