lightdm: Remove StandardOutput= configuration from service unit

From manual page systemd.exec(5):

> StandardOutput=
>     Controls where file descriptor 1 (STDOUT) of the executed processes is
>     connected to. Takes one of inherit, null, tty, journal, syslog, kmsg,
>     journal+console, syslog+console, kmsg+console, file:path, append:path, socket
>     or fd:name.
>
> […]
>
>     syslog connects standard output to the syslog(3) system syslog service, in
>     addition to the journal. Note that the journal daemon is usually configured to
>     forward everything it receives to syslog anyway, in which case this option is
>     no different from journal.

So remove the configuration.

lightdm.be0

@@ -87,7 +87,6 @@ EOF
 
 	[Service]
 	ExecStart=/usr/bin/lightdm
-	StandardOutput=syslog
 	Restart=always
 	UMask=007