cubicweb-collaboration #3670570 Collaborators can only be added, but not removed [validation pending]

Indeed, the set_collaborators adapter method can only add new collaborators to a collaborative entity.

It should first remove the old collaborators before adding new ones, so that, after each call to set_collaborators, the entity rigorously has the collaborators passed as arguments to this method.

prioritynormal
typebug
done in0.2.0
load0.150
load left0.000
closed by#8f9ee24de225 [entities] Clean up old collaborators first, before setting new ones (closes #3670570)
patch[entities] Clean up old collaborators first, before setting new ones (closes #3670570) [applied]