source_old -> source for cases that can be handled by simple bubbling

crates/hir/src/code_model.rs

@@ -1372,8 +1372,7 @@ impl Impl {
     }
 
     pub fn is_builtin_derive(self, db: &dyn HirDatabase) -> Option<InFile<ast::Attr>> {
-        #[allow(deprecated)]
-        let src = self.source_old(db);
+        let src = self.source(db)?;
         let item = src.file_id.is_builtin_derive(db.upcast())?;
         let hygenic = hir_expand::hygiene::Hygiene::new(db.upcast(), item.file_id);