Simplify ERT for TBLFM with sub-total

* testing/lisp/test-org-table.el (test-org-table/sub-total): Simplify
condition in "if".

testing/lisp/test-org-table.el

@@ -647,7 +647,7 @@ formatter \"%.1f\"."
 |-------+-------+-------|
 "
    1 (concat "#+TBLFM: @>$2 = vsum(@II..@>>) ::"
-	     "$3 = if(vlen(@-I$2..@0$2) == vlen(@-I$2..@+I$2), "
+	     "$3 = if(vlen(@0..@+I) == 1, "
 	     "vsum(@-I$2..@+I$2) +.0, string(\"\")); EN f-1 :: "
 	     "@>$3 = string(\"\")")))