[multi-sources-removal] Drop the "true" multi-sources planner Only keep copy-based sources. This will soon allow for greater code simplification. Related to #2919300

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances