docs: Add deprecation notice for repo.

[dianakhuang]

Also removes this repository from being tagged for Open edx releases.

Configuration Pull Request

Make sure that the following steps are done before merging:

• [ ] Have a Site Reliability Engineer review the PR if you don't own all of the services impacted.
• [ ] If you are adding any new default values that need to be overridden when this change goes live, update internal repos and add an entry to the top of the CHANGELOG.
• [ ] Performed the appropriate testing.
• [ ] Think about how this change will affect Open edX operators and update the wiki page for the next Open edX release if needed