[Sprint/HipsterHedgehog](bug): Removed getItemLayout() to stop FlatList related scroll bugs.

Closes #990 (closed) As far as I can tell on an Android S7 Edge running 8.0.0, there is no discernible difference in performance when scrolling by this. This needs comparing on iOS too.

__tests__/newsfeed/__snapshots__/NewsfeedList.js.snap

@@ -203,7 +203,6 @@ exports[`newsfeed list screen component should renders correctly 1`] = `
     ]
   }
   disableVirtualization={false}
-  getItemLayout={null}
   horizontal={false}
   initialNumToRender={6}
   key="f"