remove the last definition that is problematic

sample5.v

@@ -99,10 +99,3 @@ apply (redo_rev_tree_elim (fun t x => x = rev_tree t)).
 intros a t1 t2 IH1 IH2; simpl; rewrite IH1, IH2.
 easy.
 Qed.
-
-Equations redo_rev_tree' {T} (t : btree T) : btree T :=
-  redo_rev_tree' t by rec t (@ltt T) :=
-  redo_rev_tree' Leaf := Leaf ;
-  redo_rev_tree' (Node a t1 t2) := Node a (redo_rev_tree t2)
-                                        (redo_rev_tree t1).
- .