Revert "Require event format version to parse or create events"

changelog.d/4447.misc

changelog.d/4451.misc

synapse/events/__init__.py

synapse/events/builder.py

synapse/federation/federation_base.py

synapse/federation/federation_client.py

synapse/federation/federation_server.py

synapse/federation/transport/server.py

synapse/handlers/federation.py

synapse/handlers/message.py

synapse/replication/http/federation.py

synapse/replication/http/send_event.py

synapse/storage/events_worker.py

tests/storage/test_redaction.py

tests/storage/test_roommember.py

tests/storage/test_state.py

tests/test_visibility.py

tests/utils.py