cubicweb #3694139 Fix dataimport "symmetric" [validation pending]

Checking the symmetry of a relation is done by a call to rschema(rtype), and not by rschema[rtype].

prioritynormal
typebug
done in3.18.4
load0.100
load left0.000
closed by#8e9db17ce129 [dataimport] Correctly call rschema(rtype) in SqlGenObjectStore, closes #3694139
patch[dataimport] Correctly call rschema(rtype) in SqlGenObjectStore, closes #3694139 [applied]