Stop using mkdocs-macro in favour of the builtin mkdocs hooks

[pedro-psb]

I've started using mkdocs macros because it provided out-of-the-box access to mkdocs hooks without having to make a plugin. At the time, I didn't know mkdocs has a dead-simple way of defining ad-hoc hooks, which is a more standard and clean solution.

At the moment, both are being used, so I want to keep only the mkdocs way.