systemd: drop After=syslog.target rule

syslog implementations are using socket activation nowadays, so an
explicit ordering is not necessary anymore. Plus, syslog.target was
already dropped from systemd in v198.

Reported-by: Michael Biebl <biebl@debian.org>

data/ModemManager.service.in

@@ -1,6 +1,5 @@
 [Unit]
 Description=Modem Manager
-After=syslog.target
 
 [Service]
 Type=dbus