Never downgrade cells from RELAY_EARLY to RELAY.
To support v1 connections, we had a rule that any RELAY_EARLY cell sent over them had to be downgraded and sent as RELAY. Since 0.2.0.x is supposed to be dead, we can remove this. It will be needed to make legacy/trac#4339 (moved) work.
See legacy/trac#4339 (moved) for related issues. Based on a comment by wanoskarnet.