On the fsx-id branch:  Getting the commit rev from a DAG node is much
easier these days, so remove unused parts the respective private API.

* subversion/libsvn_fs_x/dag.h
  (svn_fs_x__dag_get_revision): Simplify signature.

* subversion/libsvn_fs_x/dag.c
  (svn_fs_x__dag_get_revision): Update implementation.

* subversion/libsvn_fs_x/tree.c
  (try_match_last_node,
   svn_fs_x__node_created_rev,
   x_closest_copy,
   history_prev): Update callers.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1645848 13f79535-47bb-0310-9956-ffa450edef68