[multi-sources-removal] Drop (dont_)cross relation related code
That was only needed for now deleted 'true' multisources.
Related to #2919300
[jcr: also remove it from server/test/data-schemaserial/schema.py]
#! /bin/sh -e
case "$1" in
remove)
if [ -x "/etc/init.d/cubicweb-ctl" ]; then
invoke-rc.d cubicweb-ctl stop || true
fi
;;
esac
#DEBHELPER#
exit 0