[naga] Delete unused constant Handle::DUMMY.

naga/src/arena.rs

@@ -80,12 +80,6 @@ impl<T> hash::Hash for Handle<T> {
 }
 
 impl<T> Handle<T> {
-    #[cfg(test)]
-    pub const DUMMY: Self = Handle {
-        index: unsafe { NonZeroU32::new_unchecked(u32::MAX) },
-        marker: PhantomData,
-    };
-
     pub(crate) const fn new(index: Index) -> Self {
         Handle {
             index,