[ADT] Remove ilist_default_traits

include/llvm/ADT/ilist.h

 /// A fragment for template traits for intrusive list that provides default
 /// node related operations.
 ///
 /// TODO: Remove this layer of indirection.  It's not necessary.
 template <typename NodeTy>
 struct ilist_node_traits : ilist_alloc_traits<NodeTy>,
                            ilist_callback_traits<NodeTy> {};
 
-/// Default template traits for intrusive list.
-///
-/// By inheriting from this, you can easily use default implementations for all
-/// common operations.
-///
-/// TODO: Remove this customization point.  Specializing ilist_traits is
-/// already fully general.
-template <typename NodeTy>
-struct ilist_default_traits : public ilist_node_traits<NodeTy> {};
-
 /// Template traits for intrusive list.
 ///
 /// Customize callbacks and allocation semantics.
 template <typename NodeTy>
-struct ilist_traits : public ilist_default_traits<NodeTy> {};
+struct ilist_traits : public ilist_node_traits<NodeTy> {};
 
 /// Const traits should never be instantiated.
 template <typename Ty> struct ilist_traits<const Ty> {};
 
 namespace ilist_detail {
 
 template <class T> T &make();