0635b40729
The spec says that the required signatures for a signed event is the signature of sender's server (unless is a third party invite) and the `event_id` server (in v1 and v2 room versions). This changes the previous behaviour, which tried to verify the signatures for all the servers in the `PublicKeyMap`, instead of checking only the required signatures. Relevant spec section: https://matrix.org/docs/spec/server_server/r0.1.4#validating-hashes-and-signatures-on-received-events
