change to the new "deprecated" annotation

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/safe-string@14629 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
change call to deprecated function

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/safe-string@14630 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02