Fix authentication documentation for GetPublicKey

Closes #1272 (closed)

Not much checking to do here as the endpoint has no authentication or DB access. The only important behavior is whether it retrieves the public key, and that's already tested. The only change to make is to remove the overriden authorization schemes, so that Spectacular uses its defaults. This documents that the endpoint can be accessed with no authentication at all, since "nothing" is automatically added by Spectacular.