Remove errant code

This code does not have tests and is likely unnecessary.

HandleActiveDecendant is called on the item with @aria-activedescendant,
therefore to invalidate something, followingthe forward relation is
correct. Using the reverse relation would make sense if something was
pointing at the element with @aria-activedescendant that needed
updating.

TBR=nektar@chromium.org
NOTRY=true

Bug: None
Change-Id: Ifc2e3d71a2089e5fbeb58c1bc6e020811ad9b1d6
Reviewed-on: https://chromium-review.googlesource.com/1070806
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561522}

third_party/blink/renderer/modules/accessibility/ax_layout_object.cc

@@ -2227,11 +2227,6 @@ void AXLayoutObject::HandleActiveDescendantChanged() {
   if (!GetLayoutObject())
     return;
 
-  Vector<String> ids;
-  TokenVectorFromAttribute(ids, aria_activedescendantAttr);
-  if (!ids.IsEmpty())
-    AXObjectCache().UpdateReverseRelations(this, ids);
-
   AXObject* focused_object = AXObjectCache().FocusedObject();
   if (focused_object == this && SupportsARIAActiveDescendant()) {
     AXObject* active_descendant = ActiveDescendant();