[server] remove some pre 3.10 compat
Let's assume nobody will try upgrading an instance from pre-3.10
cubicweb to 3.23+. If they do, they're setting themselves up for a lot
of pain anyway.
Schema of the data
------------------
First take a look at the data schema_ then try to remember that you are browsing
through a heap of data by applying stylesheets to the results of queries. This
site is not a content management system with items placed in folders. It is an
interface to a database which applies a view to retreived data.
.. _schema: ../schema