Don't render deprecated enum members

[lmolkova]

I think this was the intention - I don't see a reason why we want to render them (they should remain in yaml for history and codegen though). Plus it results in weird things like this #1757 (comment)

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

[arminru]

I think it's fine to not render them and by keeping them in YAML it also prevents people from accidentally re-introducing them.
Alternatively we could also render them in a separate section or move them to the end of the table, but this might just bulk up markdown further.