Remove the iOS QR Code scanner experiment code.

ios/chrome/browser/chrome_switches.h

 // 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.
 
 #ifndef IOS_CHROME_BROWSER_CHROME_SWITCHES_H_
 #define IOS_CHROME_BROWSER_CHROME_SWITCHES_H_
 
 // Defines all the command-line switches used by iOS Chrome.
 
 namespace switches {
 
 extern const char kDisableAllBookmarksView[];
 extern const char kDisableContextualSearch[];
 extern const char kDisableIOSFastWebScrollViewInsets[];
 extern const char kDisableIOSFeatures[];
 extern const char kDisableIOSPasswordGeneration[];
 extern const char kDisableIOSPasswordSuggestions[];
 extern const char kDisableLRUSnapshotCache[];
 extern const char kDisableNTPFavicons[];
 extern const char kDisableOfflineAutoReload[];
 extern const char kDisablePaymentRequest[];
-extern const char kDisableQRScanner[];
 extern const char kDisableSpotlightActions[];
 extern const char kDisableTabStripAutoScrollNewTabs[];
 extern const char kDisableTabSwitcher[];
 extern const char kDisableIOSPhysicalWeb[];
 extern const char kDisableDownloadImageRenaming[];
 
 extern const char kEnableAllBookmarksView[];
 extern const char kEnableContextualSearch[];
 extern const char kEnableCredentialManagerAPI[];
 extern const char kEnableIOSFastWebScrollViewInsets[];
 extern const char kEnableIOSFeatures[];
 extern const char kEnableIOSHandoffToOtherDevices[];
 extern const char kEnableIOSPasswordGeneration[];
 extern const char kEnableLRUSnapshotCache[];
 extern const char kEnableNTPFavicons[];
 extern const char kEnableOfflineAutoReload[];
 extern const char kEnablePaymentRequest[];
-extern const char kEnableQRScanner[];
 extern const char kEnableReaderModeToolbarIcon[];
 extern const char kEnableSpotlightActions[];
 extern const char kEnableTabSwitcher[];
 extern const char kEnableIOSPhysicalWeb[];
 extern const char kEnableDownloadImageRenaming[];
 
 extern const char kIOSForceVariationIds[];
 extern const char kIOSMetricsRecordingOnly[];
 extern const char kUserAgent[];
 
 extern const char kIOSHostResolverRules[];
 extern const char kIOSIgnoreCertificateErrors[];
 extern const char kIOSTestingFixedHttpPort[];
 extern const char kIOSTestingFixedHttpsPort[];
 
 // TODO(crbug.com/567136): this switches is duplicated between desktop
 // and iOS. Once the corresponding code has been componentized or is no longer
 // used by iOS, remove the duplicate definition.
 extern const char kHistoryEnableGroupByDomain[];
 }  // namespace switches
 
 #endif  // IOS_CHROME_BROWSER_CHROME_SWITCHES_H_