On the fsx-id branch: Get rid of the last svn_fs_id_t in our noderev struct.
It has been kept for convenience but is now hardly used anymore. Construct
the respective API object on demand.

* subversion/libsvn_fs_x/fs.h
  (node_revision_t): Drop ID member.

* subversion/libsvn_fs_x/low_level.c
  (svn_fs_x__read_noderev): One element less to initialize.

* subversion/libsvn_fs_x/noderevs.c
  (svn_fs_x__noderevs_get,
   svn_fs_x__noderevs_get_func): Same.

* subversion/libsvn_fs_x/temp_serializer.c
  (svn_fs_x__noderev_serialize,
   svn_fs_x__noderev_deserialize): One sub-struct less to (de-)serialize.

* subversion/libsvn_fs_x/dag.c
  (copy_node_revision): One element less to copy.
  (svn_fs_x__dag_get_fs_id): Construct API level ID instead of copying it.
  (svn_fs_x__dag_copy): One element less to initialize.

* subversion/libsvn_fs_x/transaction.c
  (create_new_txn_noderev_from_rev): Directly initialize the noderev-ID.
  (svn_fs_x__get_txn,
   svn_fs_x__create_node): No longer use the API level ID as intermediary.
  (svn_fs_x__add_change): Construct the API level ID on demand.
  (svn_fs_x__create_successor,
   write_final_rev: Directly assign the returned ID object.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1647131 13f79535-47bb-0310-9956-ffa450edef68