numbers.v: avoid Qed'ing Decision instances

stdpp/numbers.v

@@ -1063,13 +1063,13 @@ Module Qp.
   Global Instance le_dec : RelDecision le.
   Proof.
     refine (λ p q, cast_if (decide (Qp_to_Qc p ≤ Qp_to_Qc q)%Qc));
-      by rewrite to_Qc_inj_le.
-  Qed.
+      abstract (by rewrite to_Qc_inj_le).
+  Defined.
   Global Instance lt_dec : RelDecision lt.
   Proof.
     refine (λ p q, cast_if (decide (Qp_to_Qc p < Qp_to_Qc q)%Qc));
-      by rewrite to_Qc_inj_lt.
-  Qed.
+      abstract (by rewrite to_Qc_inj_lt).
+  Defined.
   Global Instance lt_pi p q : ProofIrrel (lt p q).
   Proof. destruct p, q; apply _. Qed.