MacViews: Consolidate flags. Just use --secondary-ui-md to enable MacViews.

chrome/browser/ui/browser_dialogs_mac.cc

-// Copyright 2015 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 "chrome/browser/ui/browser_dialogs.h"
-
-#include "base/feature_list.h"
-
-namespace chrome {
-
-const base::Feature kMacViewsNativeDialogs {
-  "MacViewsNativeDialogs", base::FEATURE_DISABLED_BY_DEFAULT
-};
-
-const base::Feature kMacViewsWebUIDialogs {
-  "MacViewsWebUIDialogs", base::FEATURE_DISABLED_BY_DEFAULT
-};
-
-bool ToolkitViewsDialogsEnabled() {
-  return base::FeatureList::IsEnabled(kMacViewsNativeDialogs);
-}
-
-bool ToolkitViewsWebUIDialogsEnabled() {
-  return base::FeatureList::IsEnabled(kMacViewsWebUIDialogs);
-}
-
-}  // namespace chrome