Remove stale FFI representation comments

Signed-off-by: Cristiano Calcagno <cristianoc@users.noreply.github.com>

Author: cristianoc

compiler/frontend/ast_external_mk.ml

@@ -78,7 +78,6 @@ let inline_string (s : string) (delim_raw : string option) =
 
 let inline_bool b = inline_const (Const_bool b)
 
-(* FIXME: check overflow ?*)
 let inline_int i = inline_const (Const_int i)
 
 let inline_bigint s =

compiler/ml/external_ffi_types.ml

@@ -36,9 +36,6 @@ type external_module_name = {
 }
 
 type arg_type = External_arg_spec.attr
-(** TODO: information between [arg_type] and [arg_label] are duplicated,
-    design a more compact representation so that it is also easy to seralize by hand
-*)
 
 type arg_label = External_arg_spec.label