Remove unused fields from ExprEvalStep

These were added recently by 1349d2790.

Reported-by: Zhihong Yu
Discussion: https://postgr.es/m/CALNJ-vTi+YDuAWKp4Z_Dv=mrz=aq81qTg0D7wzc8y7rS_+i_cw@mail.gmail.com

src/include/executor/execExpr.h

@@ -666,9 +666,6 @@ typedef struct ExprEvalStep
 		{
 			AggStatePerTrans pertrans;
 			ExprContext *aggcontext;
-			int			setno;
-			int			transno;
-			int			setoff;
 			int			jumpdistinct;
 		}			agg_presorted_distinctcheck;