[request] drop the user argument for set_session
I see no code nor test that use this optional argument. removing it help to
clean the session code. The set_session function will soon be deprecated anyway (at the
same time than the dbapi)
related to #2503918
debian/tmp/usr/bin/cubicweb-ctl usr/bin/
debian/tmp/usr/lib/PY_VERSION/site-packages/cubicweb/cwctl.py usr/lib/PY_VERSION/site-packages/cubicweb
debian/cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl