Remove the chrome flag to show/hide ARC files app in launcher.

components/arc/arc_features.cc

 // 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 "components/arc/arc_features.h"
 
 namespace arc {
 
 // Controls if ARC should use silent auth code request API.
 const base::Feature kArcUseAuthEndpointFeature {
     "ArcUseAuthEndpoint", base::FEATURE_ENABLED_BY_DEFAULT
 };
 
 // Controls ACTION_BOOT_COMPLETED broadcast for third party applications on ARC.
 // When disabled, third party apps will not receive this broadcast.
 const base::Feature kBootCompletedBroadcastFeature {
     "ArcBootCompletedBroadcast", base::FEATURE_ENABLED_BY_DEFAULT
 };
 
-// Controls whether we show ARC Files app in Chrome launcher.
-const base::Feature kShowArcFilesAppFeature {
-    "ShowArcFilesApp", base::FEATURE_DISABLED_BY_DEFAULT
-};
-
 }  // namespace arc