remove Obj_empty_cst which is dead code

Author: bobzhang

jscomp/core/lam_compile_external_obj.ml

@@ -49,7 +49,7 @@ let assemble_obj_args (labels : External_arg_spec.obj_params)  (args : J.express
     | {obj_arg_label = Label {name = label; cst = Some cst }} :: labels  , args -> 
       let accs, eff, assign = aux labels args in 
       (label, Lam_compile_const.translate_arg_cst cst )::accs, eff, assign 
-    | {obj_arg_label = EmptyCst _ } :: rest  , args -> assert false 
+    (* | {obj_arg_label = EmptyCst _ } :: rest  , args -> assert false  *)
     | {obj_arg_label = Empty  }::labels, arg::args 
       ->  (* unit type*)
       let (accs, eff, assign) as r  = aux labels args in 

jscomp/syntax/external_arg_spec.ml

@@ -41,7 +41,7 @@ type label_noname =
 type label = 
   | Label of {name : string ; cst : cst option }
   | Empty 
-  | EmptyCst of cst 
+  (* | EmptyCst of cst  *)
   | Optional of {name : string }
   (* it will be ignored , side effect will be recorded *)
 
@@ -106,7 +106,7 @@ let cst_json (loc : Location.t) s : cst  =
 let cst_int i = Arg_int_lit i 
 let cst_string s = Arg_string_lit s 
 let empty_label = Empty 
-let empty_lit s = EmptyCst s
+(* let empty_lit s = EmptyCst s *)
 let label name cst = Label {name ; cst}
 let optional name = Optional {name}
 

jscomp/syntax/external_arg_spec.mli

@@ -34,7 +34,7 @@ type cst = private
 type label = private
   | Label of {name : string ; cst : cst option }
   | Empty 
-  | EmptyCst of cst
+  (* | EmptyCst of cst *)
   | Optional of {name : string}
   (* it will be ignored , side effect will be recorded *)
 
@@ -75,7 +75,7 @@ val cst_int : int -> cst
 val cst_string : string -> cst 
 
 val empty_label : label
-val empty_lit : cst -> label 
+(* val empty_lit : cst -> label  *)
 val label :  string -> cst option -> label
 val optional  : string -> label
 val empty_kind : attr -> obj_param