In FSX, eliminate the representation's uniquifier.

This makes svn_fs_contents_changed and svn_fs_props_changed return FALSE
even if there have been intermediate changes that were later undone.
Because this is consistent with the API docstrings and our usage of these
functions, there is no need for the uniquifier storage overhead.

* subversion/libsvn_fs_x/fs.h
  (representation_t): Drop uniquifier member.

* subversion/libsvn_fs_x/fs_x.c
  (svn_fs_x__noderev_same_rep_key): Two references to the same physically
                                    representaion are now the "same".

* subversion/libsvn_fs_x/low_level.c
  (svn_fs_x__parse_representation,
   svn_fs_x__unparse_representation): Remove uniquifier (de-)serialization
                                      code.

* subversion/libsvn_fs_x/noderevs.c
  (shared_representation_t): This indirection struct is no longer needed.
  (binary_noderev_t): Directly reference the representation.
  (svn_fs_x__noderevs_add,
   svn_fs_x__noderevs_get,
   svn_fs_x__noderevs_get_func): Update container internal struct <->
                                 external struct conversion.
  (svn_fs_x__write_noderevs_container,
   svn_fs_x__read_noderevs_container): Update container (de-)serialization.

* subversion/libsvn_fs_x/transaction.c
  (set_uniquifier): Drop this now pointless utility function.
  (svn_fs_x__set_entry,
   get_shared_rep,
   rep_write_contents_close): Remove uniquifier setting code.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1568600 13f79535-47bb-0310-9956-ffa450edef68