The v3 api was sunset at the end of July 2023. This PR cleans up code
related to api v3.
## Pull Request Checklist
- [ ] The Certbot team has recently expressed interest in reviewing a PR
for this. If not, this PR may be closed due our limited resources and
need to prioritize how we spend them.
- [ ] If the change being made is to a [distributed
component](https://certbot.eff.org/docs/contributing.html#code-components-and-layout),
edit the `main` section of `certbot/CHANGELOG.md` to include a
description of the change being made.
- [ ] Add or update any documentation as needed to support the changes
in this PR.
- [ ] Include your name in `AUTHORS.md` if you like.
* certbot-dns-linode : Added support for linode version 4 tokens
* certbot-dns-linode : Added credentials ini option to override automatic api version detection
* certbot-dns-linode : Added clearer messages and documentation based on review
* certbot-dns-linode : Added check for empty 'linode_version' config instead of missing
* certbot-dns-linode : Fix rebase on master
* certbot-dns-linode : Updated local-oldest-requirements.txt
* Updated CHANGELOG to indicate Linode v4 API key support
