[connection] eliminate ClientConnection leftovers * in the documentation * in the docstrings * in code notations (e.g. clt_cnx -> cnx) Related to #3837233. From now, there should be just one ClientConnection left in repoapi.py.

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