doc: remove superfluous URL require statement

Since v10.0.0, the `URL` class is available on the global object, so
using a `require` statement to access it is no longer necessary.

PR-URL: https://github.com/nodejs/node/pull/20364


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>