[cwconfig] Remove useless 'ui-cube' configuration option (closes #3728904) The mechanism introduced could never actually be used as it brings dependency loops to the cube graph. Just get rid of it. This reverts commit 4032499c701e.

# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s specific hooks and operations"""