FederationDeniedError is not a SynapseError.

Basically the same reasoning that @erikjohnston gave in #13816 (comment)

I'm not sure it makes sense for this to inherit from SynapseError. The risk is that this manages to bubble all the way to the client API, returning a 403, which seems entirely wrong.

See #14191 where SynapseError is given more context and clarified.

Todo

• Make sure any upstream callers handle FederationDeniedError properly and not just the inherited SynapseError class

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