Example pages and Index page: remove extraneous broken link and navigation region from end of main content

[mcking65]

On the index page, and on all example pages,
there is a nav element at the end of the main content containing a single link
named "WAI-ARIA Authoring Practices 1.2".

The link is broken, and because it is in a nav element, it is prominent for screen reader users. We need to remove the nav element and link. I think we should do this before launch.

The question is whether to filter it out during build or remove it from the roughly 60 pages that contain it in the aria-practices source repo. Eventually we definitely need to remove it from the source. Should we bite the bullet and do that now? Or add some filtering code to the build?

[mcking65]

Verified fixed in #62 preview.