Remove TrayPopupLabelButton (a pre-MD class) and its assets.

ash/common/system/tray/tray_popup_label_button.cc

Index: ash/common/system/tray/tray_popup_label_button.cc
diff --git a/ash/common/system/tray/tray_popup_label_button.cc b/ash/common/system/tray/tray_popup_label_button.cc
deleted file mode 100644
index 1289cd67bd79e0170cd8e0a8798b0f53d8bc458c..0000000000000000000000000000000000000000
--- a/ash/common/system/tray/tray_popup_label_button.cc
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "ash/common/system/tray/tray_popup_label_button.h"
-
-#include "ash/common/ash_constants.h"
-#include "ash/common/material_design/material_design_controller.h"
-#include "ash/common/system/tray/tray_popup_label_button_border.h"
-#include "ui/gfx/canvas.h"
-#include "ui/gfx/geometry/rect.h"
-#include "ui/views/painter.h"
-
-namespace ash {
-
-TrayPopupLabelButton::TrayPopupLabelButton(views::ButtonListener* listener,
-                                           const base::string16& text)
-    : views::LabelButton(listener, text) {
-  DCHECK(!MaterialDesignController::IsSystemTrayMenuMaterial());
-  SetBorder(std::unique_ptr<views::Border>(new TrayPopupLabelButtonBorder));
-  SetFocusForPlatform();
-  set_animate_on_state_change(false);
-  SetHorizontalAlignment(gfx::ALIGN_CENTER);
-  SetFocusPainter(views::Painter::CreateSolidFocusPainter(
-      kFocusBorderColor, gfx::Insets(1, 1, 2, 2)));
-}
-
-TrayPopupLabelButton::~TrayPopupLabelButton() {}
-
-}  // namespace ash