Fix a typo in close_functions.

(Patch by Evgeny Roubinchtein)

The typo isn't a bug since the variables `arity' and `body' are never
actually referenced in the body of the function, but it does
(negatively) affect readability of the code.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14430 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02