Deprecating the version 2 documentation

[kathryn-ods]

@greggish and I have been discussing removing v2.0 documentation from https://docs.openreferral.org/

I’ve been working on some changes to the documentation to clearly signpost to the latest version of the docs in response to SEO: Many top hits for HSDS search terms go to v2.0 docs

As v2.0 hasn’t been worked on in more than 5 years, making any updates to the documentation means tackling all the technical debt that has accumulated in that time. It would be more efficient to only link to v3.0 and v3.1 on the docs site.

Would anyone here object to that?