Clean up some code for new MSRV (#1888)

Also clean up some code for 0.9.

src/lib.rs

@@ -395,27 +395,6 @@ const _: () = {
     _WARNING
 };
 
-// These exist so that code which was written against the old names will get
-// less confusing error messages when they upgrade to a more recent version of
-// zerocopy. On our MSRV toolchain, the error messages read, for example:
-//
-//   error[E0603]: trait `FromZeroes` is private
-//       --> examples/deprecated.rs:1:15
-//        |
-//   1    | use zerocopy::FromZeroes;
-//        |               ^^^^^^^^^^ private trait
-//        |
-//   note: the trait `FromZeroes` is defined here
-//       --> /Users/josh/workspace/zerocopy/src/lib.rs:1845:5
-//        |
-//   1845 | use FromZeros as FromZeroes;
-//        |     ^^^^^^^^^^^^^^^^^^^^^^^
-//
-// The "note" provides enough context to make it easy to figure out how to fix
-// the error.
-#[allow(unused)]
-use {FromZeros as FromZeroes, IntoBytes as AsBytes, Ref as LayoutVerified};
-
 /// Implements [`KnownLayout`].
 ///
 /// This derive analyzes various aspects of a type's layout that are needed for

src/pointer/ptr.rs

@@ -120,7 +120,6 @@ mod def {
     }
 }
 
-#[allow(unreachable_pub)] // This is a false positive on our MSRV toolchain.
 pub use def::Ptr;
 
 /// Used to define the system of [invariants][invariant] of `Ptr`.

src/wrappers.rs

@@ -239,11 +239,7 @@ impl<T> Unalign<T> {
         // but the caller has promised that `self` is properly aligned, so we
         // know that it is sound to create a reference to `T` at this memory
         // location.
-        //
-        // We use `mem::transmute` instead of `&*self.get_ptr()` because
-        // dereferencing pointers is not stable in `const` on our current MSRV
-        // (1.56 as of this writing).
-        unsafe { mem::transmute(self) }
+        unsafe { &*self.get_ptr() }
     }
 
     /// Returns a mutable reference to the wrapped `T` without checking