Remove some unused FSX code.

* subversion/libsvn_fs_x/tree.c
  (is_changed_node): Remove.

* subversion/libsvn_fs_x/hotcopy.c
  (hotcopy_body, hotcopy_locking_src_body): Remove unused variable.

* subversion/libsvn_fs_x/index.c
  (p2l_entries_func): Remove unused variable.

* subversion/libsvn_fs_x/transaction.c
  (svn_fs_x__with_all_locks,
   rep_write_contents_close,
   write_final_changed_path_info): Remove unused variable.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1602359 13f79535-47bb-0310-9956-ffa450edef68