Fix header formatting in Sphinx-based docs

https://github.com/freeCodeCamp/devdocs/blob/58a0120697a701f2cb9ca87061ec7ef6fde3b013/lib/docs/filters/sphinx/clean_html.rb#L64

However, this is not entirely desirable since the formatting makes things look better. For example, the [header for `BaseException`](http://devdocs.localhost/python~3.8/library/exceptions#BaseException) ([original](https://docs.python.org/3.8/library/exceptions.html#BaseException)) is transformed from this:

> *exception* **`BaseException`**

to this:
> `exception BaseException`

cc @Thibaut since you might have a reason for implementing this this way. (no worries if you don’t reply though)