[tracking] Phase out legacy chat #3043

We have been default-on with the new chat for two releases now and have heard no complaints yet. Thus assuming that this is acceptable already and people are not switching back to the old chat. Let's put up a timeline to remove the old chat and thus reduce our code a lot.

This also acts as the anchor point for people to let us know if they still need the legacy chat and why they have switched that on. If you are any of those people, please comment below or send us a message (via email or any support chat channels).

Proposed timeline

• May 30th: Announce timeline
• June 13th: End of Request for comments
  Consultation and review of the feedback given. If nothing major is blocking the timeline will proceed
• June 20th (nightly) / June 26th (release): removing of legacy chat from the code base

If we will find any major reason in the consultation period to postpone the final removal, we might be delaying that milestone until those are resolved, keeping the legacy chat around as a fallback for the people who need it.