dbus.service.in: Do not order after syslog.target

dbus.service.in: Do not order after syslog.target

It is no longer required or recommended in fact it no longer
exists since
http://cgit.freedesktop.org/systemd/systemd/commit/?id=5d4caf565471ff3401bd9b53aa814c8545a18a93

[Clarification: there are two reasons why we do not need that dependency.
First, we do not have DefaultDependencies=no, so we only get run after
sockets.target. Second, syslog.socket doesn't provide /dev/log, which is
part of systemd-journald.socket. -smcv]

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=63531
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>