[multi-sources-removal] Drop pyrorql and zmqrql sources
After a few years experementing "true" multi-sources, we're now
moving to "copy-based" source à la datafeed.
As pyro and zmq sources have no more known customers and the related
code is in the way of future refactoring of cubicweb's core, we decided
to drop support for those sources without backward compatibility.
If you're still using a zmqrql or pyrorql source and you want to upgrade,
ask support to move it to datafeed using a pre-3.19 version first.
Related to #2919300 (first step)