fin_sets: add missing Params instance for `set_map`

Noticed from VERY slow rewrites.

theories/fin_sets.v

@@ -23,6 +23,7 @@ Definition set_map `{Elements A C, Singleton B D, Empty D, Union D}
     (f : A → B) (X : C) : D :=
   list_to_set (f <$> elements X).
 Typeclasses Opaque set_map.
+Global Instance: Params (@set_map) 8 := {}.
 
 Global Instance set_fresh `{Elements A C, Fresh A (list A)} : Fresh A C :=
   fresh ∘ elements.