archive(8.1) isolation: remove all other versions

[pepopowitz]

Note that this PR targets unsupported/8.1, and will never make it into main!

Description

Part of #3731.

This is the Chonky Boi ™️ PR for isolating version 8.1, in which all other versions are removed from the unsupported/8.1 branch.

We will merge this PR in a red state, as it requires follow-up steps to fix the build.

Removes:

• docs/version-1.3
• docs/version-8.2
• docs/version-8.3
• docs/version-8.4
• docs/version-8.5
• docs/next
• optimize/version-3.10.0
• optimize/version-3.11.0
• optimize/version-3.12.0
• optimize/version-3.13.0
• optimize/version-3.7.0
• optimize/next

Description

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• There is no urgency with this change and can be released at any time.
• My goal is to complete archival of 8.1 by the end of this week (May 3). I'd like to merge this in the next day to meet this schedule.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineerring DRI or delegate.
• My changes require a technical writer review, and I've assigned @christinaausley as a reviewer.

[akeller]

This is a handwavy review, because my computer is exploding but I see that you didn't add anything and it's going to a separate branch (as in, not main). 🪄