drop some const unstables, due to revert no longer possible

Author: Mark-Simulacrum

library/core/src/mem/mod.rs

@@ -682,8 +682,7 @@ pub unsafe fn uninitialized<T>() -> T {
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
-pub const fn swap<T>(x: &mut T, y: &mut T) {
+pub fn swap<T>(x: &mut T, y: &mut T) {
     // SAFETY: the raw pointers have been created from safe mutable references satisfying all the
     // constraints on `ptr::swap_nonoverlapping_one`
     unsafe {
@@ -813,8 +812,7 @@ pub fn take<T: Default>(dest: &mut T) -> T {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[must_use = "if you don't need the old value, you can just assign the new value directly"]
-#[rustc_const_unstable(feature = "const_replace", issue = "83164")]
-pub const fn replace<T>(dest: &mut T, src: T) -> T {
+pub fn replace<T>(dest: &mut T, src: T) -> T {
     // SAFETY: We read from `dest` but directly write `src` into it afterwards,
     // such that the old value is not duplicated. Nothing is dropped and
     // nothing here can panic.

library/core/src/ptr/mod.rs

@@ -463,8 +463,7 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
 }
 
 #[inline]
-#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
-pub(crate) const unsafe fn swap_nonoverlapping_one<T>(x: *mut T, y: *mut T) {
+pub(crate) unsafe fn swap_nonoverlapping_one<T>(x: *mut T, y: *mut T) {
     // For types smaller than the block optimization below,
     // just swap directly to avoid pessimizing codegen.
     if mem::size_of::<T>() < 32 {

library/core/src/ptr/mut_ptr.rs

@@ -1013,9 +1013,8 @@ impl<T: ?Sized> *mut T {
     ///
     /// [`ptr::write`]: crate::ptr::write()
     #[stable(feature = "pointer_methods", since = "1.26.0")]
-    #[rustc_const_unstable(feature = "const_ptr_write", issue = "none")]
     #[inline]
-    pub const unsafe fn write(self, val: T)
+    pub unsafe fn write(self, val: T)
     where
         T: Sized,
     {