Remove duplicate signature due to an ocaml 3.07 problem

this patch probably makes cduce inomcpatible with ocaml 3.07

types/types.ml

@@ -133,13 +133,7 @@ type pair_kind = [ `Normal | `XML ]
 
 module rec Descr : 
 sig
-(*
-  Want to write:
-    type s = { ... }
-    include Custom.T with type t = s
-  but a  bug (?) in OCaml 3.07 makes it impossible
-*)
-  type t = {
+  type s = {
     atoms : Atoms.t;
     ints  : Intervals.t;
     chars : Chars.t;
@@ -150,15 +144,12 @@ sig
     abstract: Abstract.t;
     absent: bool
   }
+
+  include Custom.T with type t = s
   val empty: t
-  val dump: Format.formatter -> t -> unit
-  val check: t -> unit
-  val equal: t -> t -> bool
-  val hash: t -> int
-  val compare:t -> t -> int
 end =
 struct
-  type t = {
+  type s = {
     atoms : Atoms.t;
     ints  : Intervals.t;
     chars : Chars.t;
@@ -169,6 +160,7 @@ struct
     abstract: Abstract.t;
     absent: bool
   }
+  type t = s
 
   let print_lst ppf =
     List.iter (fun f -> f ppf; Format.fprintf ppf " |")