Removal: Remove support for experimental msc3886

[rahulporuri]

fixes #17619

Pull Request Checklist

• [x] Pull request is based on the develop branch
• [x] Pull request includes a changelog file. The entry should:
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[anoadragon453]

Hi @rahulporuri, are you willing to finish this one off? It doesn't need much more!

[rahulporuri]

sorry for the radio silence @anoadragon453 , will wrap things up tomorrow/weekend. I hope that's okay. I'll update this and my other PR too.

[anoadragon453]

Certainly! Thank you :)

[anoadragon453]

Hi @rahulporuri, do you have time to finish this PR? Otherwise I'm happy to take it over to get it over the line. Thanks!

[rahulporuri]

please take over @anoadragon453 :pray: I haven't been able to make time and I doubt I will be able to discover any free time this weekend either :/ . I sincerely apologize for not being able to get this past the finish line

[anoadragon453]

That's alright @rahulporuri, life happens! The team is grateful to you for kicking off this effort in the first place :slightly_smiling_face:

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