Remove box syntax from rustc_builtin_macros

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -179,7 +179,7 @@ fn inject_impl_of_structural_trait(
         span,
         Ident::invalid(),
         attrs,
-        ItemKind::Impl(box ImplKind {
+        ItemKind::Impl(Box::new(ImplKind {
             unsafety: ast::Unsafe::No,
             polarity: ast::ImplPolarity::Positive,
             defaultness: ast::Defaultness::Final,
@@ -188,7 +188,7 @@ fn inject_impl_of_structural_trait(
             of_trait: Some(trait_ref),
             self_ty: self_type,
             items: Vec::new(),
-        }),
+        })),
     );
 
     push(Annotatable::Item(newitem));