revert a lia back to omega

Author: kim-em

Mathlib/Data/Int/Interval.lean

@@ -57,7 +57,7 @@ instance instLocallyFiniteOrder : LocallyFiniteOrder ℤ where
     · lia
     · intro
       use (x - (a + 1)).toNat
-      lia
+      omega
   finset_mem_Ioo a b x := by
     simp_rw [mem_map, mem_range, Function.Embedding.trans_apply, Nat.castEmbedding_apply,
       addLeftEmbedding_apply]