Avoid redefining rle type in modified run-length exercice (ocaml#476)

Co-authored-by: Thibaut Mattio <thibaut.mattio@gmail.com>

data/problems/011_modified_run_length.md

@@ -35,6 +35,7 @@ elements with duplicates are transferred as (N E) lists.
 Since OCaml lists are homogeneous, one needs to define a type to hold
 both single elements and sub-lists.
 
+<!-- $MDX skip -->
 ```ocaml
 type 'a rle =
   | One of 'a
@@ -43,7 +44,7 @@ type 'a rle =
 
 ```ocaml
 # encode ["a"; "a"; "a"; "a"; "b"; "c"; "c"; "a"; "a"; "d"; "e"; "e"; "e"; "e"];;
-- : string rle/2 list =
+- : string rle list =
 [Many (4, "a"); One "b"; Many (2, "c"); Many (2, "a"); One "d";
  Many (4, "e")]
 ```