As part of the harmony UX rollout, we are also removing the join feature in the MR dialog. There are 2 items we can simplify / remove:

- There won't be a need for supporting the sourceId parameter in a route query. It was used by the dialog to determine what routes are joinable with the sourceId. As a bonus, since the route query will become parameter-less with the change, we can consider removing the route query API and just always have MediaRouteProvider implementations supply route updates.

- ConnectRouteByRouteId, the MediaRouter API used by the MR dialog to implement join, can be deprecated / removed with the harmony UX rollout. Although there were plans to actually replace JoinRoute with ConnectRouteByRouteId, we need to work out how the Cast autojoin will work with the new API. The simplest, though hacky way would be for MediaRouter to check for the "autojoin" presentation ID and a Cast presentation URL.