Fixs tests for updated report label

internal/driver/testdata/pprof.cpusmall.flat.addresses.tree

 Showing nodes accounting for 4s, 100% of 4s total
-Showing top 4 nodes out of 5 (cum >= 2s)
+Showing top 4 nodes out of 5
 ----------------------------------------------------------+-------------
       flat  flat%   sum%        cum   cum%   calls calls% + context 	 	 
 ----------------------------------------------------------+-------------

internal/report/report.go

 		}
 		if nodeCount > 0 && nodeCount < origCount {
 			label = append(label, fmt.Sprintf("Showing top %d nodes out of %d",
-				nodeCount, origCount,
-				rpt.formatValue(g.Nodes[len(g.Nodes)-1].Cum)))
+				nodeCount, origCount))
 		}
 	}
 	return label