doc: remove warning from response.writeHead

The example referenced as being potentially unsafe specifies
Content-Length correctly.

PR-URL: #32700
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>

doc/api/http.md

@@ -1713,12 +1713,10 @@ const server = http.createServer((req, res) => {
 });
 ```
 
-`Content-Length` is given in bytes not characters. The above example
-works because the string `'hello world'` contains only single byte characters.
-If the body contains higher coded characters then `Buffer.byteLength()`
-should be used to determine the number of bytes in a given encoding.
-And Node.js does not check whether `Content-Length` and the length of the body
-which has been transmitted are equal or not.
+`Content-Length` is given in bytes, not characters. Use
+[`Buffer.byteLength()`][] to determine the length of the body in bytes. Node.js
+does not check whether `Content-Length` and the length of the body which has
+been transmitted are equal or not.
 
 Attempting to set a header field name or value that contains invalid characters
 will result in a [`TypeError`][] being thrown.
@@ -2388,6 +2386,7 @@ not abort the request or do anything besides add a `'timeout'` event.
 [`'response'`]: #http_event_response
 [`'upgrade'`]: #http_event_upgrade
 [`Agent`]: #http_class_http_agent
+[`Buffer.byteLength()`]: buffer.html#buffer_class_method_buffer_bytelength_string_encoding
 [`Duplex`]: stream.html#stream_class_stream_duplex
 [`TypeError`]: errors.html#errors_class_typeerror
 [`URL`]: url.html#url_the_whatwg_url_api