rustc_metadata: Make attribute decoding slightly faster and stricter

Rename `CStore::item_attrs` -> `CStore::item_attrs_untracked` top follow conventions

compiler/rustc_resolve/src/lib.rs

@@ -3420,7 +3420,7 @@ impl<'a> Resolver<'a> {
 
                 let attr = self
                     .cstore()
-                    .item_attrs(def_id, self.session)
+                    .item_attrs_untracked(def_id, self.session)
                     .into_iter()
                     .find(|a| a.has_name(sym::rustc_legacy_const_generics))?;
                 let mut ret = Vec::new();