Remove obsolete class DownstreamChromiumBrowserProvider.

ios/chrome/browser/downstream_chromium_browser_provider_factory.mm

Index: ios/chrome/browser/downstream_chromium_browser_provider_factory.mm
diff --git a/ios/chrome/browser/downstream_chromium_browser_provider_factory.mm b/ios/chrome/browser/downstream_chromium_browser_provider_factory.mm
deleted file mode 100644
index 06eb39a54e59c2f99a1b304c51dcea3e56c36b4f..0000000000000000000000000000000000000000
--- a/ios/chrome/browser/downstream_chromium_browser_provider_factory.mm
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright 2016 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 "base/memory/ptr_util.h"
-#include "ios/chrome/browser/downstream_chromium_browser_provider.h"
-#include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
-
-namespace ios {
-std::unique_ptr<ChromeBrowserProvider> CreateChromeBrowserProvider() {
-  return base::MakeUnique<DownstreamChromiumBrowserProvider>();
-}
-}  // namespace ios