Demo: Demonstrate out-of-order rendering using ImDrawListSplitter.

imgui.h

@@ -2706,7 +2706,7 @@ struct ImDrawList
     // Advanced: Channels
     // - Use to split render into layers. By switching channels to can render out-of-order (e.g. submit FG primitives before BG primitives)
     // - Use to minimize draw calls (e.g. if going back-and-forth between multiple clipping rectangles, prefer to append into separate channels then merge at the end)
-    // - FIXME-OBSOLETE: This API shouldn't have been in ImDrawList in the first place!
+    // - This API shouldn't have been in ImDrawList in the first place!
     //   Prefer using your own persistent instance of ImDrawListSplitter as you can stack them.
     //   Using the ImDrawList::ChannelsXXXX you cannot stack a split over another.
     inline void     ChannelsSplit(int count)    { _Splitter.Split(this, count); }