[repo, hooks] small task optimization: don't start cleanup_old_transactions when undo support is not activated, and retrieve a session to update a source only when some source to update is found

#! /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