osmo-trap2cgi: Remove invalid specifier for /etc

On prod-bscnat the specifier %E (for /etc) does not exist so let's not
use it.

Change-Id: Ia3d8838475c2cc8f9f4ba3a0bc5483c6e1645f8f
Related: SYS#4399

contrib/systemd/osmo-trap2cgi.service

@@ -4,7 +4,7 @@ Description=Proxy between given GCI service and Osmocom CTRL protocol
 [Service]
 Type=simple
 Restart=always
-ExecStart=/usr/bin/osmo_trap2cgi.py -d -c %E/osmocom/%N.ini
+ExecStart=/usr/bin/osmo_trap2cgi.py -d -c /etc/osmocom/%N.ini
 RestartSec=2
 
 [Install]