chore: remove tmi endpoints

[Nerixyz]

The TMI endpoints were shut down in April 2023. This removes the feature.

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Aside:

• I think we should aim for a release soon. The last release was almost seven months ago.
• It might be nice if Client::req could use RPITIT, although it requires quite the MSRV bump from 1.65 to 1.75.
• EventsubWebsocketData::Notification (and ::Revocation) should have some better type for payload like NotificationEvent, since the Payload's message can only be of one type at that point. It's not super visible in the example, but if you wanted to do something with the message, you'd need to match/if-let on it again.
• We should consider if eventsub enums like Message should be marked non_exhaustive. Although it's nice for the library to be able to add variants and not break semver, it might be better for a user to get a compile error when updating and not handling an added variant (it's fine for enums like Event).

[Emilgardis]

We have an issue for RPITIT

I agree with the payload enum being very annoying. If a way to improve it is possible we should aim to do that, should make an issue for it. Same goes for non_exhaustive on message

I want to do a real release, I'm only thinking about if #359 should be included or not.