Begin making auth use event.old_state_events

synapse/api/auth.py

synapse/handlers/_base.py

synapse/handlers/directory.py

synapse/handlers/federation.py

synapse/handlers/message.py

synapse/handlers/profile.py

synapse/handlers/room.py

synapse/state.py

synapse/storage/schema/state.sql

synapse/storage/state.py