On the fsx-id branch: Simplify FS API ID comparison code for FSX.

* subversion/libsvn_fs_x/id.c
  (svn_fs_x__id_eq): Since the noderev ID is already unique,
                     we only need to compare that.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1645672 13f79535-47bb-0310-9956-ffa450edef68