We no longer allow early-boot init scripts, however in late boot the
syslog socket and local mounts are established anyway, so let's simplify
our dep graph a bit.

If $syslog doesn't resolve to syslog.target anymore there's no reason to
keep syslog.target around anymore. Let's remove it.

Note that many 3rd party service unit files order themselves after
syslog.target. These will be dangling dependencies now, which should be
unproblematic, however.