[test] drop CubicWebConfigurationWithLegacyCubesTC
This is used to test legacy cube import which is planned for removal
in cubicweb 3.27, so drop the code.
.. _cwprops:
The property mecanism
---------------------
.. XXX CWProperty and co
Property API
~~~~~~~~~~~~
.. XXX feed me
Registering and using your own property
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. XXX feed me