v2v: Hide StringMap functions we're not actually using.

In RHEL 6 OCaml, some of these functions were not part of the Map
class, giving an error.  Hide the ones we aren't using.

v2v/stringMap.mli

@@ -23,13 +23,18 @@ val empty : 'a t
 val is_empty : 'a t -> bool
 val mem : key -> 'a t -> bool
 val add : key -> 'a -> 'a t -> 'a t
+(*
 val singleton : key -> 'a -> 'a t
+*)
 val remove : key -> 'a t -> 'a t
+(*
 val merge : (key -> 'a option -> 'b option -> 'c option) -> 'a t -> 'b t -> 'c t
+*)
 val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
 val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
 val iter : (key -> 'a -> unit) -> 'a t -> unit
 val fold : (key -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
+(*
 val for_all : (key -> 'a -> bool) -> 'a t -> bool
 val exists : (key -> 'a -> bool) -> 'a t -> bool
 val filter : (key -> 'a -> bool) -> 'a t -> 'a t
@@ -40,7 +45,10 @@ val min_binding : 'a t -> key * 'a
 val max_binding : 'a t -> key * 'a
 val choose : 'a t -> key * 'a
 val split : key -> 'a t -> 'a t * 'a option * 'a t
+*)
 val find : key -> 'a t -> 'a
 val map : ('a -> 'b) -> 'a t -> 'b t
+(*
 val mapi : (key -> 'a -> 'b) -> 'a t -> 'b t
+*)
 val keys : 'a t -> key list