Remove now unused Cell and SyncUnsafeCell diagnostic item

Author: Urgau

compiler/rustc_span/src/symbol.rs

@@ -171,7 +171,6 @@ symbols! {
         CallOnceFuture,
         CallRefFuture,
         Capture,
-        Cell,
         Center,
         Cleanup,
         Clone,
@@ -316,7 +315,6 @@ symbols! {
         SubdiagMessage,
         Subdiagnostic,
         Sync,
-        SyncUnsafeCell,
         T,
         Target,
         ToOwned,

library/core/src/cell.rs

@@ -304,7 +304,6 @@ pub use once::OnceCell;
 /// ```
 ///
 /// See the [module-level documentation](self) for more.
-#[cfg_attr(not(test), rustc_diagnostic_item = "Cell")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[repr(transparent)]
 #[rustc_pub_transparent]
@@ -2274,7 +2273,6 @@ impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T>
 /// See [`UnsafeCell`] for details.
 #[unstable(feature = "sync_unsafe_cell", issue = "95439")]
 #[repr(transparent)]
-#[rustc_diagnostic_item = "SyncUnsafeCell"]
 #[rustc_pub_transparent]
 pub struct SyncUnsafeCell<T: ?Sized> {
     value: UnsafeCell<T>,