- Feature removal:
    - When sending or relaying a RELAY_EARLY cell, we used to convert
      it to a RELAY cell if the connection was using the v1 link
      protocol. This was a workaround for older versions of Tor, which
      didn't handle RELAY_EARLY cells properly. Now that all supported
      versions can handle RELAY_EARLY cells, and now that we're
      enforcing the "no RELAY_EXTEND commands except in RELAY_EARLY
      cells" rule, we're removing this workaround. Addresses bug 4786.