[low] link to old WAI presentation page

[shawna-slh]

https://www.w3.org/WAI/teach-advocate/accessible-presentations/#expres says:

Make provided material accessible If you are giving participants material, make it accessible. See provide accessible material above. An example of presentation material provided in both presentation format and web format (HTML and CSS) is linked from the top of the page after “The Benefits of WCAG 2 presentation is available in 2 formats:”.

It links to an old page. Let's consider:

• When will we have an updated example to point to?
• What should we do in the meantime -- delete the link or leave it?