We should add a bit of UI to let the user tell the client to forget about one of the accounts it's logged into.

This can be helpful for decluttering the list of accounts, after logging into some test account or some other account one doesn't expect to use again.

In zulip-mobile we have this in the form of a red trash-can icon on each of the accounts in the list. I don't love that UI and we can probably do something better.