109.20.00

- Removed some warnings caused by generated signatures.

  1. In signatures on local modules.
  2. When there are duplicate signature items like in this example:

    ```ocaml
    module Warnings : sig
      type t = private { foo : int } with fields (** used to say unused value foo *)
      val foo : string
    end = struct
      type t = { foo : int } with fields
      let foo = "a"
    end
    ```

  3. In the signatures of all the parameters of functors that take multiple
     parameters; this used to work only for the last parameter.