Some exiled lemmas about casting

These lemmas have been removed from Mathlib.Data.Rat.Cast.Defs to avoiding needing to import Mathlib.Algebra.Field.Basic there.

In fact, these lemmas don't appear to be used anywhere in Mathlib, so perhaps this file can simply be deleted.

@[simp]

theorem Rat.cast_inv_nat {α : Type u_1} [DivisionRing α] (n : ℕ) : ↑(↑n)⁻¹ = (↑n)⁻¹

@[simp]

theorem Rat.cast_inv_int {α : Type u_1} [DivisionRing α] (n : ℤ) : ↑(↑n)⁻¹ = (↑n)⁻¹