[gardening] Remove unneeded method addNodeToList on ilist_traits<SILBasicBlock>.

addNodeToList only needs to be implemented to override the default callback
behavior of ilist_trait_defaults<SILBasicBlock>.  This implmentation in
ilist_traits<SILBasicBlock> is exactly the same as the default callback so is
unnecessary.

Author: gottesmm

include/swift/SIL/SILBasicBlock.h

@@ -425,11 +425,8 @@ struct ilist_traits<::swift::SILBasicBlock>
 public:
   static void deleteNode(SILBasicBlock *BB) { BB->~SILBasicBlock(); }
 
-  void addNodeToList(SILBasicBlock *BB) {}
-
   void transferNodesFromList(ilist_traits<SILBasicBlock> &SrcTraits,
                              block_iterator First, block_iterator Last);
-
 private:
   static void createNode(const SILBasicBlock &);
 };