Goptions.declare_* functions return unit instead of a write_function

Returning a writer insinuates that it is not exactly the same as the
writer which was passed as argument, but that is incorrect.

library/goptions.ml

@@ -276,10 +276,7 @@ let declare_option cast uncast append ?(preprocess = fun x -> x)
   let cread () = cast (read ()) in
   let cwrite l v = warn (); change l OptSet (uncast v) in
   let cappend l v = warn (); change l OptAppend (uncast v) in
-  value_tab := OptionMap.add key (name, depr, (cread,cwrite,cappend)) !value_tab;
-  write
-
-type 'a write_function = 'a -> unit
+  value_tab := OptionMap.add key (name, depr, (cread,cwrite,cappend)) !value_tab
 
 let declare_int_option =
   declare_option

library/goptions.mli

@@ -122,16 +122,14 @@ type 'a option_sig = {
 (** The [preprocess] function is triggered before setting the option. It can be
     used to emit a warning on certain values, and clean-up the final value. *)
 
-type 'a write_function = 'a -> unit
-
 val declare_int_option   : ?preprocess:(int option -> int option) ->
-                           int option option_sig -> int option write_function
+                           int option option_sig -> unit
 val declare_bool_option  : ?preprocess:(bool -> bool) ->
-                           bool option_sig   -> bool write_function
+                           bool option_sig   -> unit
 val declare_string_option: ?preprocess:(string -> string) ->
-                           string option_sig -> string write_function
+                           string option_sig -> unit
 val declare_stringopt_option: ?preprocess:(string option -> string option) ->
-                              string option option_sig -> string option write_function
+                              string option option_sig -> unit
 
 
 (** {6 Special functions supposed to be used only in vernacentries.ml } *)

tactics/class_tactics.ml

@@ -113,7 +113,7 @@ let _ =
       optread  = get_typeclasses_filtered_unification;
       optwrite = set_typeclasses_filtered_unification; }
 
-let set_typeclasses_debug =
+let _ =
   declare_bool_option
     { optdepr  = false;
       optname  = "debug output for typeclasses proof search";
@@ -137,7 +137,7 @@ let _ =
       optread  = get_typeclasses_verbose;
       optwrite = set_typeclasses_verbose; }
 
-let set_typeclasses_depth =
+let _ =
   declare_int_option
     { optdepr  = false;
       optname  = "depth for typeclasses proof search";