doc: remove linking of url text to url

Linking URL text to itself is superfluous. It will display as a link in
GitHub anyway. Bonus: This makes it possible to wrap the line at 80
characters.

PR-URL: https://github.com/nodejs/node/pull/21361


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>