TT#177600 Remove unused files from /etc/ngcp-config/

The factory_default files are not created anymore by the installer,
and the systems.cfg file is neither created by the installer nor
needed or used since commit 5e2037cf82.

Change-Id: I9c58021db307f23923b4cfee8a1862561dc09d3d

debian/ngcp-ngcpcfg.postinst

@@ -14,6 +14,11 @@ case "$1" in
       fi
 
       addgroup --system --force-badname --quiet _ngcp-admin
+
+      # Since mr10.5.
+      rm -f /etc/ngcp-config/config.yml.factory_default
+      rm -f /etc/ngcp-config/network.yml.factory_default
+      rm -f /etc/ngcp-config/systems.cfg
     ;;
 
     abort-upgrade|abort-remove|abort-deconfigure)