[DOCS] Remove Kythera AI Documentation From Main Docs Site

[ShaunaGordon]

Describe the issue briefly

The Steering Committee and previous docs maintainers decided to not include detailed documentation about third party gems in the main site. Additionally, part of the requirements for 3rd Party assets to be included is that the asset in question must be freely available. Kythera recently transitioned to a paid offering, making it no longer qualify as approvable even if we allowed 3rd Party assets. Therefore, I propose that we remove the Kythera tutorials, at least from the main O3DE docs site.

It does feel kind of bad to remove the content wholesale, though. I think we'll want to reach out to the Kythera team to see if they have better resources hosted somewhere else these days, or if they even want the information out there anymore.

Which page(s) / section(s) are affected?

https://docs.o3de.org/docs/user-guide/gems/reference/kythera-ai/

Does this work have an engineering dependency? What is it?

No known dependencies

[ShaunaGordon]

I've reached out to Kythera via their contact form (the Discord members that advertise themselves as part of the Kythera team all show as offline, and the last post from any of them was 2022, with most ending in 2021) to see if they want to keep any of what we have, and if they want us to link to anything they have. Will update if/when I get a response.