[ash-md] Removed unwanted TODO from ShelfWidget::DelegateView::opaque_background_

ash/shelf/shelf_widget.cc

Index: ash/shelf/shelf_widget.cc
diff --git a/ash/shelf/shelf_widget.cc b/ash/shelf/shelf_widget.cc
index ded98373f428f414c434283d811199ebc894c013..22ada4835a0e507fb566a3fcbcfc57fce4ddcec2 100644
--- a/ash/shelf/shelf_widget.cc
+++ b/ash/shelf/shelf_widget.cc
@@ -66,7 +66,6 @@ class ShelfWidget::DelegateView : public views::WidgetDelegate,
   FocusCycler* focus_cycler_;
   // A black background layer that may be visible depending on a
   // ShelfBackgroundAnimator.
-  // TODO(bruthig): Remove opaque_background_ (see https://crbug.com/621551).
   ui::Layer opaque_background_;
   // A black foreground layer which is shown while transitioning between users.
   // Note: Since the back- and foreground layers have different functions they