doc: update url.origin IDNA behavior

Fixes: 413691fde0 "url: expose WHATWG url.origin as ASCII"
PR-URL: https://github.com/nodejs/node/pull/14478
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

doc/api/url.md

@@ -211,9 +211,7 @@ will be thrown.
 
 * {string}
 
-Gets the read-only serialization of the URL's origin. Unicode characters that
-may be contained within the hostname will be encoded as-is without [Punycode][]
-encoding.
+Gets the read-only serialization of the URL's origin.
 
 ```js
 const { URL } = require('url');
@@ -226,7 +224,7 @@ console.log(myURL.origin);
 const { URL } = require('url');
 const idnURL = new URL('https://你好你好');
 console.log(idnURL.origin);
-// Prints https://你好你好
+// Prints https://xn--6qqa088eba
 
 console.log(idnURL.hostname);
 // Prints xn--6qqa088eba