Revert of cc: Add a main thread LayerListIterator

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 47691bf9e2b47ae6f6ba51f0a1f1679f3a334710..17b1e6b8301ff32ad5edb80b4d1a7a7e668f03e8 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -900,22 +900,6 @@
   bool result = DoUpdateLayers(root_layer());
   micro_benchmark_controller_.DidUpdateLayers();
   return result || next_commit_forces_redraw_;
-}
-
-LayerListIterator<Layer> LayerTreeHost::begin() {
-  return LayerListIterator<Layer>(root_layer_.get());
-}
-
-LayerListIterator<Layer> LayerTreeHost::end() {
-  return LayerListIterator<Layer>(nullptr);
-}
-
-LayerListReverseIterator<Layer> LayerTreeHost::rbegin() {
-  return LayerListReverseIterator<Layer>(root_layer_.get());
-}
-
-LayerListReverseIterator<Layer> LayerTreeHost::rend() {
-  return LayerListReverseIterator<Layer>(nullptr);
 }
 
 void LayerTreeHost::DidCompletePageScaleAnimation() {