cubicweb #5168939 remove test dependency on folder cube [validation pending]

Test dependencies on downstream projects (cubes here) should be limited as much as possible (I think there's an agreement on this, for various reasons). Plus this would simplify a bit the setup of a cubicweb development environment.

prioritynormal
typebug
done in3.21.0
load0.500
load left0.000
closed by#593e63a68429 [server/test] Drop dependency on folder cube
patch[server/test] Drop dependency on folder cube [applied][web/test] Drop folder cube dependency [applied]