MacOS warnings buildbot.

Found

r1821858

r1821858 | julianfoad | 2018-01-22 12:47:45 +0000 (Mon, 22 Jan 2018)

Don't use deprecated functions.

Found by: MacOS warnings buildbot.

* subversion/svn/shelf-cmd.c
  (run_status_on_wc_paths,
   check_no_modified_paths): s/svn_path_join/svn_dirent_join/.