In ra-serf, don't declare xml attributes which are never used in the dav
protocol.

* subversion/libsvn_ra_serf/update.c
  (update_ttable): Don't define rev as valid property for add-file/-dir
    as they don't use this. Don't declare the unused bc-url for files, as
    it is only provided on dirs.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1608742 13f79535-47bb-0310-9956-ffa450edef68