Bug 1861854 - remove outdated links r=sylvestre DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D192483

docs/setup/contributing_code.rst

@@ -172,10 +172,5 @@ to the project. We'll be integrating some information from these pages
 soon, but until then you may find them interesting in their current
 form:
 
--  `A guide to learning the Firefox
-   codebase <http://www.joshmatthews.net/blog/2010/03/getting-involve-with-mozilla/>`_
 -  `A beginner's guide to SpiderMonkey, Mozilla's Javascript
    engine <https://wiki.mozilla.org/JavaScript:New_to_SpiderMonkey>`_
--  `Mozilla platform development
-   cheatsheet <https://web.archive.org/web/20160813112326/http://www.codefirefox.com:80/cheatsheet>`_
-   (archive.org)