doc: "if and only if" should be "if" in util.parseArgs default value

The default value is legal by means other than defaulting.

Author: Slayer95

doc/api/util.md

@@ -1956,7 +1956,7 @@ changes:
       `false`, values for the option are last-wins. **Default:** `false`.
     * `short` {string} A single character alias for the option.
     * `default` {string | boolean | string\[] | boolean\[]} The default value to
-      be used if (and only if) the option does not appear in the arguments to be
+      be used if the option does not appear in the arguments to be
       parsed. It must be of the same type as the `type` property. When `multiple`
       is `true`, it must be an array.
   * `strict` {boolean} Should an error be thrown when unknown arguments