add () to the marker_impls macro for ConstParamTy

seems to have escaped bootstrap

library/core/src/marker.rs

@@ -996,15 +996,12 @@ marker_impls! {
         bool,
         char,
         str /* Technically requires `[u8]: ConstParamTy` */,
+        (),
         {T: ConstParamTy, const N: usize} [T; N],
         {T: ConstParamTy} [T],
         {T: ?Sized + ConstParamTy} &T,
 }
 
-// FIXME(adt_const_params): Add to marker_impls call above once not in bootstrap
-#[unstable(feature = "adt_const_params", issue = "95174")]
-impl ConstParamTy for () {}
-
 /// A common trait implemented by all function pointers.
 #[unstable(
     feature = "fn_ptr_trait",