chore: remove mkAppN macro in omega (#3428)

src/Lean/Elab/Tactic/Omega/Frontend.lean

@@ -76,13 +76,6 @@ def mkAtomLinearCombo (e : Expr) : OmegaM (LinearCombo × OmegaM Expr × HashSet
   let (n, facts) ← lookup e
   return ⟨LinearCombo.coordinate n, mkCoordinateEvalAtomsEq e n, facts.getD ∅⟩
 
--- This has been PR'd as
--- https://github.com/leanprover/lean4/pull/2900
--- and can be removed when that is merged.
-@[inherit_doc mkAppN]
-local macro_rules
-  | `(mkAppN $f #[$xs,*]) => (xs.getElems.foldlM (fun x e => `(Expr.app $x $e)) f : MacroM Term)
-
 mutual
 
 /--
@@ -221,7 +214,7 @@ partial def asLinearComboImpl (e : Expr) : OmegaM (LinearCombo × OmegaM Expr ×
     | (``HDiv.hDiv, #[_, _, _, _, a, b]) => rewrite e (mkApp2 (.const ``Int.ofNat_ediv []) a b)
     | (``OfNat.ofNat, #[_, n, _]) => rewrite e (.app (.const ``Int.natCast_ofNat []) n)
     | (``HMod.hMod, #[_, _, _, _, a, b]) => rewrite e (mkApp2 (.const ``Int.ofNat_emod []) a b)
-    | (``HSub.hSub, #[_, _, _, _, mkAppN (.const ``HSub.hSub _) #[_, _, _, _, a, b], c]) =>
+    | (``HSub.hSub, #[_, _, _, _, mkApp6 (.const ``HSub.hSub _) _ _ _ _ a b, c]) =>
       rewrite e (mkApp3 (.const ``Int.ofNat_sub_sub []) a b c)
     | (``Prod.fst, #[_, β, p]) => match p with
       | .app (.app (.app (.app (.const ``Prod.mk [0, v]) _) _) x) y =>