cubicweb #2535376 tests: consider windmill removal [validation pending]

looks like a failed experiment to me

* windmill is not packaged in debian
* tests are broken for more than two years (they are not even run)

prioritynormal
typeenhancement
done in3.17.4
load0.200
load left0.000
closed by#a71d3928443b [test] drop forsaken windmill test (Closes 2535376)