Cite stable docs for bit validity of numeric types (#1869)

src/impls.rs

@@ -38,15 +38,12 @@ safety_comment! {
  /// - The only value >= 1 for which 1 is an integer multiple is 1
  /// Therefore, the only possible alignment for `u8` and `i8` is 1.
  ///
- /// [1] Per https://doc.rust-lang.org/beta/reference/types/numeric.html#bit-validity:
+ /// [1] Per https://doc.rust-lang.org/1.81.0/reference/types/numeric.html#bit-validity:
  ///
  /// For every numeric type, `T`, the bit validity of `T` is equivalent to
  /// the bit validity of `[u8; size_of::<T>()]`. An uninitialized byte is
  /// not a valid `u8`.
  ///
- /// TODO(https://github.com/rust-lang/reference/pull/1392): Once this text
- /// is available on the Stable docs, cite those instead.
- ///
  /// [2] https://doc.rust-lang.org/1.81.0/reference/type-layout.html#primitive-data-layout
  ///
  /// [3] Per https://doc.rust-lang.org/1.81.0/reference/type-layout.html#size-and-alignment: