Remove wait_for_disconnection

[bdraco]

This issue is for tracking purposes only so we don't forget

          > I'm not sure its useful, but I've also never had a use case for it. I'd open an issue to provide notice of intent to remove it, and than do so in 30 days if nobody objects.

Well, it's only been in a release for a week or so. So, it's incredibly unlikely people are already using it, we can probably just strip in the next 3.10 release before most users have finished upgrading to 3.10.

Originally posted by @Dreamsorcerer in #8611 (comment)