don't encode only locally used attrs

compiler/rustc_middle/src/query/mod.rs

@@ -1072,6 +1072,9 @@ rustc_queries! {
         desc { |tcx| "checking whether `{}` is `doc(hidden)`", tcx.def_path_str(def_id) }
     }
 
+    /// Returns the attributes on the item at `def_id`.
+    ///
+    /// Do not use this directly, use `tcx.get_attrs` instead.
     query item_attrs(def_id: DefId) -> &'tcx [ast::Attribute] {
         desc { |tcx| "collecting attributes of `{}`", tcx.def_path_str(def_id) }
         separate_provide_extern