Remove docs/containers for insecure releases

### description

checking the docs page, i think some of the docs relate to builds/releases for which there are known sec issues:

https://www.envoyproxy.io/docs

(also, some of the links are dead)

afaict there are also still dockerhub images with a similar issue:

https://hub.docker.com/r/envoyproxy/envoy/tags?page=1&ordering=last_updated&name=1.17

if you read the docs and look at the published images there is no way of knowing that some versions should be avoided

imho we should probably just delete all images and docs other than the latest for each minor version