Remove misleading ?Sized bound

clippy output:

warning: `?Sized` bound is ignored because of a `Sized` requirement
  --> src/lib.rs:81:17
   |
81 | impl<T: Clone + ?Sized> Clone for AlignedBox<T> {
   |                 ^^^^^^
   |
note: `T` cannot be unsized because of the bound
  --> src/lib.rs:81:9
   |
81 | impl<T: Clone + ?Sized> Clone for AlignedBox<T> {
   |         ^^^^^
   = note: ...because `Clone` has the bound `Sized`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_maybe_sized
   = note: `#[warn(clippy::needless_maybe_sized)]` on by default
help: change the bounds that require `Sized`, or remove the `?Sized` bound
   |
81 - impl<T: Clone + ?Sized> Clone for AlignedBox<T> {
81 + impl<T: Clone> Clone for AlignedBox<T> {
   |

src/lib.rs

@@ -78,7 +78,7 @@ impl<T: ?Sized> Drop for AlignedBox<T> {
     }
 }
 
-impl<T: Clone + ?Sized> Clone for AlignedBox<T> {
+impl<T: Clone> Clone for AlignedBox<T> {
     fn clone(&self) -> Self {
         // SAFETY:
         // layout is certainly valid as it has already been used to create self