Remove debugging symbols in failwith

As running `OCAMLRUNPARAM=b ./_build/main.native ...` provides in case of `failwith` a better stacktrace.
This enables moving `failwith`s from a file to the other without adapting them.

src/main.ml

@@ -35,7 +35,7 @@ let exec_passes ast verbose debug passes f =
                 "Current AST (after %s):\n%a\n" n Lustre_pp.pp_ast ast);
             aux ast passes)
         end with
-        | _ -> failwith ("[main.ml] The pass "^n^" should have catched me!")
+        | _ -> failwith ("The pass "^n^" should have catched me!")
   in
   aux ast passes