Dont use `unimplemented!()` macro as it causes federation breakages.

[Nutomic]

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Summary

https://github.com/LemmyNet/lemmy/blob/0.19.3/crates/apub/src/activities/block/mod.rs#L79

This code gets called by the federation library here when receiving a ban action in a removed community. Need to replace it with something like the following:

    match apub {
      InstanceOrGroup::Instance(i) => Site::delete(...).await,
      InstanceOrGroup::Group(g) => Instance::delete(...).await,
    }

We should deny the macro via clippy to ensure it isnt used anywhere in the code. Same goes for todo!() macro.

Edit: Specifically InstanceOrGroup should use a macro, such as enum_delegate which is already used elsewhere. Same for PostOrComment and the other ones next to it.