remove retag_box_to_raw, it is no longer needed

Author: RalfJung

core/src/intrinsics.rs

@@ -2709,19 +2709,6 @@ pub unsafe fn vtable_size(_ptr: *const ()) -> usize {
     unreachable!()
 }
 
-/// Retag a box pointer as part of casting it to a raw pointer. This is the `Box` equivalent of
-/// `(x: &mut T) as *mut T`. The input pointer must be the pointer of a `Box` (passed as raw pointer
-/// to avoid all questions around move semantics and custom allocators), and `A` must be the `Box`'s
-/// allocator.
-#[unstable(feature = "core_intrinsics", issue = "none")]
-#[rustc_nounwind]
-#[cfg_attr(not(bootstrap), rustc_intrinsic)]
-#[cfg_attr(bootstrap, inline)]
-pub unsafe fn retag_box_to_raw<T: ?Sized, A>(ptr: *mut T) -> *mut T {
-    // Miri needs to adjust the provenance, but for regular codegen this is not needed
-    ptr
-}
-
 // Some functions are defined here because they accidentally got made
 // available in this module on stable. See <https://github.com/rust-lang/rust/issues/15702>.
 // (`transmute` also falls into this category, but it cannot be wrapped due to the