chore(data/nat/factorization): golf dvd_iff_prime_pow_dvd_dvd (#13473)

Golfing the edge-case proof added in #13316

src/data/nat/factorization.lean

@@ -293,17 +293,11 @@ end
 lemma dvd_iff_prime_pow_dvd_dvd (n d : ℕ) :
   d ∣ n ↔ ∀ p k : ℕ, prime p → p ^ k ∣ d → p ^ k ∣ n :=
 begin
-  by_cases hn : n = 0,
-  { simp [hn], },
-  by_cases hd : d = 0,
-  { simp only [hd, hn, zero_dvd_iff, dvd_zero, forall_true_left, false_iff,
-      not_forall, exists_prop, exists_and_distrib_left],
-    refine ⟨2, prime_two, n, λ h, _⟩,
-    have := le_of_dvd (nat.pos_of_ne_zero hn) h,
-    revert this,
-    change ¬ _,
-    rw [not_le],
-    exact lt_two_pow n, },
+  rcases eq_or_ne n 0 with rfl | hn, { simp },
+  rcases eq_or_ne d 0 with rfl | hd,
+  { simp only [zero_dvd_iff, hn, false_iff, not_forall],
+    refine ⟨2, n, prime_two, ⟨dvd_zero _, _⟩⟩,
+    apply mt (le_of_dvd hn.bot_lt) (not_le.mpr (lt_two_pow n)) },
   refine ⟨λ h p k _ hpkd, dvd_trans hpkd h, _⟩,
   rw [←factorization_le_iff_dvd hd hn, finsupp.le_def],
   intros h p,