systemd service file: Stop using deprecated '-e' option

In commit 6d8884de490d09902e9e31a90bab9ef490ef5d82 in 2014, we
made the '-e' command line option deprecated.  Stop using it from the
systemd srevice file.

Change-Id: I322cadbee8980b78fff2984765c4b0216c50412e
Related: SYS#2749
diff --git a/contrib/sysmopcu.service b/contrib/sysmopcu.service
index d4585cc..3e3ff07 100644
--- a/contrib/sysmopcu.service
+++ b/contrib/sysmopcu.service
@@ -3,7 +3,7 @@
 
 [Service]
 Type=simple
-ExecStart=/usr/bin/osmo-pcu -c /etc/osmocom/osmo-pcu.cfg -e
+ExecStart=/usr/bin/osmo-pcu -c /etc/osmocom/osmo-pcu.cfg
 Restart=always
 RestartSec=2
 RestartPreventExitStatus=1