Deprecate :> for typeclasses?

Author: proux01

vernac/record.ml

@@ -867,7 +867,9 @@ let class_structure ~cumulative ~template ~impargs ~univs ~params ~primitive_pro
   in
   let coers = List.map (fun (_, { rf_subclass; rf_priority }) ->
       match rf_subclass with
-      | Vernacexpr.BackInstance -> Some {hint_priority = rf_priority; hint_pattern = None}
+      | Vernacexpr.BackInstance ->
+         assert false
+         (* Some {hint_priority = rf_priority; hint_pattern = None} *)
       | Vernacexpr.NoInstance -> None)
       cfs
   in