speed up f_equiv by doing reflexivity less often

theories/list.v

@@ -3113,7 +3113,7 @@ Section mapM.
     (∀ x y, f y = Some x → y = g x) → mapM f k = Some l → k = g <$> l.
   Proof.
     intros Hgf. revert l; induction k as [|??]; intros [|??] ?;
-      simplify_option_eq; f_equiv; eauto.
+      simplify_option_eq; try f_equiv; eauto.
   Qed.
 End mapM.
 

theories/tactics.v

@@ -272,7 +272,6 @@ when having [Proper (equiv ==> dist) f] and [Proper (dist ==> dist) f], it will
 favor the second because the relation (dist) stays the same. *)
 Ltac f_equiv :=
   match goal with
-  | _ => reflexivity
   | |- pointwise_relation _ _ _ _ => intros ?
   (* We support matches on both sides, *if* they concern the same variable, or
      variables in some relation. *)