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 64210cc4b4c60f83a77e404edf1eca9f1fb585a6..e10dd3fe2c0ce4767f508bb63aa5620246a9cd16 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -897,22 +897,6 @@
   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() {