Remove a mostly unused kind variable from the merge target baton.

* subversion/libsvn_client/merge.c
  (merge_target_t): Remove kind.
  (do_merge): Remove kind check.
  (open_target_wc): Return an error when the target is not versioned instead
    of asking this from the caller.
  (svn_client_find_automatic_merge_no_wc): Don't fill value.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1442530 13f79535-47bb-0310-9956-ffa450edef68