cubicweb-mercurial-server #2800705 remove useless exception [validation pending]

NoCommitNeeded sits there, likely unused

prioritynormal
typebug
done in0.2.1
load0.100
load left0.000
closed by#0c7319a97de6 [entities] remove useless exception (closes #2800705)
patch[entities] remove useless exception (closes #2800705) [applied]