cubicweb-seda #12515386 skip group handling for now [validation pending]

we decided that group handling could be skipped for now, simplify the schema accordingly.

prioritynormal
typeenhancement
done in0.2.0
load left0.000
closed by#e33cf4cf19fb [xsd2yams] Skip data object group handling
patch[xsd2yams] Skip data object group handling [applied]