doc: remove misleading paragraph about the Legacy URL API

The Legacy URL API is deprecated, see:

- https://nodejs.org/api/url.html#url_legacy_url_api
- https://nodejs.org/api/deprecations.html#
deprecations_dep0116_legacy_url_api

PR-URL: https://github.com/nodejs/node/pull/29844


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>