Remove Invariant_env, empty invariant checks, etc. (ocaml-flambda#265)

Author: mshinwell

middle_end/flambda2/basic/exn_continuation.ml

@@ -85,8 +85,6 @@ let exn_handler t = t.exn_handler
 
 let extra_args t = t.extra_args
 
-let invariant _env _t = ()
-
 let free_names { exn_handler; extra_args } =
   let extra_args = List.map (fun (simple, _kind) -> simple) extra_args in
   Name_occurrences.union

middle_end/flambda2/basic/exn_continuation.mli

@@ -23,7 +23,6 @@
 
 type t
 
-(** Printing, invariant checks, name manipulation, etc. *)
 include Container_types.S with type t := t
 
 include Expr_std.S with type t := t

middle_end/flambda2/basic/expr_std.ml

@@ -24,7 +24,5 @@ module type S = sig
 
   val print_with_cache : cache:Printing_cache.t -> Format.formatter -> t -> unit
 
-  val invariant : Invariant_env.t -> t -> unit
-
   include Contains_names.S with type t := t
 end