cubicweb #1796196 facets should drop groupby from prepared rqlst [resolved]

as we search for values for a variable, there seems to be no case where we would be interested in groups

prioritynormal
typebug
done in3.12.9
load0.100
load left0.000
closed by#9030e8a4481e [facets] should remove groupby from base rqlst. Closes #1796196