Remove node-origin FSFS backward compat code from FSX.
Our data model always provides the copy root info that
would be missing in old FSFS formats.

* subversion/libsvn_fs_x/util.h
  (svn_fs_x__path_node_origin): Drop. We don't need that cache file.

* subversion/libsvn_fs_x/util.c
  (svn_fs_x__path_node_origin): Same.

* subversion/libsvn_fs_x/fs_x.h
  (svn_fs_x__get_node_origin,
   svn_fs_x__set_node_origin): Drop. Nobody calls these.

* subversion/libsvn_fs_x/fs_x.c
  (get_node_origins_from_file,
   svn_fs_x__get_node_origin,
   set_node_origins_for_file,
   svn_fs_x__set_node_origin): Remove their implemenation as well.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1595088 13f79535-47bb-0310-9956-ffa450edef68