[test] Drop call to CubicWebConfiguration.load_cwctl_plugins in unittest_cwctl.py This is no longer need now that we call load_available_configurations() in the "list" command (see 5e7282bdf140).

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))