Remove implementation of Deref

According to the Rust docs [0] on the `Deref` trait, it should only be
implemented for smart pointers.

Remove the implementation of `Deref`.

[0] https://doc.rust-lang.org/std/ops/trait.Deref.html

Author: tcharding

src/util.rs

@@ -25,9 +25,9 @@ macro_rules! hex_fmt_impl(
                 use $crate::{Hash as _, HashEngine as _, hex};
 
                 if $ty::<$($gen),*>::DISPLAY_BACKWARD {
-                    hex::format_hex_reverse(&self.0, f)
+                    hex::format_hex_reverse(self.as_ref(), f)
                 } else {
-                    hex::format_hex(&self.0, f)
+                    hex::format_hex(self.as_ref(), f)
                 }
             }
         }
@@ -52,14 +52,6 @@ macro_rules! borrow_slice_impl(
                 &self[..]
             }
         }
-
-        impl<$($gen: $gent),*> $crate::_export::_core::ops::Deref for $ty<$($gen),*> {
-            type Target = [u8];
-
-            fn deref(&self) -> &Self::Target {
-                &self.0
-            }
-        }
     )
 );
 
@@ -295,7 +287,7 @@ mod test {
     fn borrow_slice_impl_to_vec() {
         // Test that the borrow_slice_impl macro gives to_vec.
         let hash = sha256::Hash::hash(&[3, 50]);
-        assert_eq!(hash.to_vec().len(), sha256::Hash::LEN);
+        assert_eq!(hash.as_ref().len(), sha256::Hash::LEN);
     }
 
     #[test]