o Minor features (relay):
    - When choosing which circuits can be expired as unused, consider
      circuits from clients even if those clients used regular CREATE
      cells to make them; and do not consider circuits from relays even if
      they were made with CREATE_FAST. Part of ticket 22805.

  o Code simplification and refactoring:
    - Remove various ways of testing circuits and connections for
      "clientness"; instead, favor channel_is_client().
      Part of ticket 22805.