Remove last MD reference from TrayPopupUtils.

ui/views/BUILD.gn

Index: ui/views/BUILD.gn
diff --git a/ui/views/BUILD.gn b/ui/views/BUILD.gn
index 9012fe50657e48656cad30f36d4734994a6471d4..cd2138d061c2fb53707aebf1cff6ded6de5b6d66 100644
--- a/ui/views/BUILD.gn
+++ b/ui/views/BUILD.gn
@@ -167,8 +167,6 @@ component("views") {
     "controls/link.cc",
     "controls/link.h",
     "controls/link_listener.h",
-    "controls/md_slider.cc",
-    "controls/md_slider.h",
     "controls/menu/display_change_listener_mac.cc",
     "controls/menu/menu_config.cc",
     "controls/menu/menu_config.h",
@@ -222,8 +220,6 @@ component("views") {
     "controls/native/native_view_host.h",
     "controls/native/native_view_host_mac.h",
     "controls/native/native_view_host_mac.mm",
-    "controls/non_md_slider.cc",
-    "controls/non_md_slider.h",
     "controls/prefix_delegate.h",
     "controls/prefix_selector.cc",
     "controls/prefix_selector.h",
@@ -720,8 +716,6 @@ static_library("test_support_internal") {
     "test/test_layout_manager.cc",
     "test/test_layout_manager.h",
     "test/test_platform_native_widget.h",
-    "test/test_slider.cc",
-    "test/test_slider.h",
     "test/test_views.cc",
     "test/test_views.h",
     "test/test_views_delegate.h",