Remove deprecated declarations.

Keep `.whereNotNull`. It's deprecation is fairly new.
Deprecate `IterableZip` in anticipation of getting `.zip`
in the platform libraries.

Author: lrhn

pkgs/collection/lib/src/queue_list.dart

@@ -5,10 +5,6 @@
 import 'dart:collection';
 
 /// A class that efficiently implements both [Queue] and [List].
-// TODO(nweiz): Currently this code is copied almost verbatim from
-// dart:collection. The only changes are to implement List and to remove methods
-// that are redundant with ListMixin. Remove or simplify it when issue 21330 is
-// fixed.
 interface class QueueList<E> with ListMixin<E> implements Queue<E> {
   /// Adapts [source] to be a `QueueList<T>`.
   ///