Related to DOM nodes accumulation in memory while scrolling in DynamicSizeList.

[dheerajk30]

@bvaughn I was checking out the demo of DynamicSizeList here(https://react-window-next.now.sh/#/examples/list/dynamic-size) when I noticed that there is a memory leak in scrolling effect as the DOM nodes are increasing while scrolling but they don't get garbage collected somehow. I started from DOM nodes count ~2000 and after scrolling for some time, it increased to ~9000 and never went back to the initial count. This will become very problematic when the user is continously scrolling through the app. I checked if the same issue is there in FixedSizeList or DynamicSizeList but it is not there

[BrianHung]

I see a memory leak in DOM Nodes with the FixedSizeList on that example page as well: the number of DOM Nodes linearly increases until I stop scrolling, and then drops after afterwards. Oddly enough, on the code sandbox example, there isn't a memory leak.