Remove no-longer-necessary MakePolymorphicRefCounted().

src/core/ext/filters/client_channel/client_channel_channelz.cc

@@ -105,8 +105,8 @@ grpc_arg ClientChannelNode::CreateChannelArg() {
 RefCountedPtr<ChannelNode> ClientChannelNode::MakeClientChannelNode(
     grpc_channel* channel, size_t channel_tracer_max_nodes,
     bool is_top_level_channel) {
-  return MakePolymorphicRefCounted<ChannelNode, ClientChannelNode>(
-      channel, channel_tracer_max_nodes, is_top_level_channel);
+  return MakeRefCounted<ClientChannelNode>(channel, channel_tracer_max_nodes,
+                                           is_top_level_channel);
 }
 
 }  // namespace channelz

src/core/lib/gprpp/ref_counted_ptr.h

@@ -154,11 +154,6 @@ inline RefCountedPtr<T> MakeRefCounted(Args&&... args) {
   return RefCountedPtr<T>(New<T>(std::forward<Args>(args)...));
 }
 
-template <typename Parent, typename Child, typename... Args>
-inline RefCountedPtr<Parent> MakePolymorphicRefCounted(Args&&... args) {
-  return RefCountedPtr<Parent>(New<Child>(std::forward<Args>(args)...));
-}
-
 }  // namespace grpc_core
 
 #endif /* GRPC_CORE_LIB_GPRPP_REF_COUNTED_PTR_H */