Removed many pointless calls to *iter() and iter_mut()

src/libsyntax/fold.rs

@@ -353,7 +353,7 @@ pub fn noop_fold_view_path<T: Folder>(view_path: P<ViewPath>, fld: &mut T) -> P<
 }
 
 pub fn fold_attrs<T: Folder>(attrs: Vec<Attribute>, fld: &mut T) -> Vec<Attribute> {
-    attrs.into_iter().flat_map(|x| fld.fold_attribute(x).into_iter()).collect()
+    attrs.into_iter().flat_map(|x| fld.fold_attribute(x)).collect()
 }
 
 pub fn noop_fold_arm<T: Folder>(Arm {attrs, pats, guard, body}: Arm, fld: &mut T) -> Arm {