Remove stale TODO in PropertyTreeManager::CreateCompositorScrollNode

non_fast_scrollable_region has been moved onto cc::Layer and no longer
needs to be set from PropertyTreeManager::CreateCompositorScrollNode.

Change-Id: I36419beb55980b102de1c818cf9e6b5bf301bffb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2083385
Commit-Queue: Philip Rogers <pdr@chromium.org>
Commit-Queue: Stefan Zager <szager@chromium.org>
Auto-Submit: Philip Rogers <pdr@chromium.org>
Reviewed-by: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746180}

third_party/blink/renderer/platform/graphics/compositing/property_tree_manager.cc

@@ -571,8 +571,6 @@ void PropertyTreeManager::CreateCompositorScrollNode(
 
   compositor_node.transform_id = scroll_offset_translation.id;
 
-  // TODO(pdr): Set the scroll node's non_fast_scrolling_region value.
-
   scroll_node.SetCcNodeId(new_sequence_number_, id);
 
   GetScrollTree().SetScrollOffset(compositor_element_id,