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 bbf338bfa1786f4a4e651264b6336065c9006964..4ba14ce5062c6769a82dd338078c0f9a7f069f16 100644
--- a/ui/views/BUILD.gn
+++ b/ui/views/BUILD.gn
@@ -161,8 +161,6 @@ 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",
@@ -216,8 +214,6 @@ 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",
@@ -717,8 +713,6 @@ 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",