[repository] when deleting relations of a deleted external entity, we should skip non-crossable relation (closes #1973680) elses this may lead to things as described in the ticket...

#! /bin/sh -e
 
case "$1" in
    purge)
	rm -rf /etc/cubicweb.d/
	rm -rf /var/log/cubicweb/
	rm -rf /var/lib/cubicweb/
    ;;
esac
 
#DEBHELPER#
 
exit 0