Remove the iOS QR Code scanner experiment code.

ios/chrome/browser/about_flags.mm

 // Copyright 2012 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.
 
 // Implementation of about_flags for iOS that sets flags based on experimental
 // settings.
 
 #include "ios/chrome/browser/about_flags.h"
 
 #include <stddef.h>
@@ skipping 209 matching lines @@
     int32_t major = 0;
     int32_t minor = 0;
     int32_t bugfix = 0;
     base::SysInfo::OperatingSystemVersionNumbers(&major, &minor, &bugfix);
     std::string product = base::StringPrintf("Version/%d.%d", major, minor);
 
     command_line->AppendSwitchASCII(switches::kUserAgent,
                                     web::BuildUserAgentFromProduct(product));
   }
 
-  // Populate command line flags from QRScanner.
-  if ([defaults boolForKey:@"DisableQRCodeReader"]) {
-    command_line->AppendSwitch(switches::kDisableQRScanner);
-  } else {
-    command_line->AppendSwitch(switches::kEnableQRScanner);
-  }
-
   // Populate command line flag for the Payment Request API.
   NSString* enable_payment_request =
       [defaults stringForKey:@"EnablePaymentRequest"];
   if ([enable_payment_request isEqualToString:@"Enabled"]) {
     command_line->AppendSwitch(switches::kEnablePaymentRequest);
   } else if ([enable_payment_request isEqualToString:@"Disabled"]) {
     command_line->AppendSwitch(switches::kDisablePaymentRequest);
   }
 
   // Populate command line flag for Spotlight Actions.
@@ skipping 96 matching lines @@
 }
 
 namespace testing {
 
 const flags_ui::FeatureEntry* GetFeatureEntries(size_t* count) {
   *count = arraysize(kFeatureEntries);
   return kFeatureEntries;
 }
 
 }  // namespace testing