Remove deprecated version of PaymentResponse::ToDictionaryValue.

ios/web/payments/payment_request.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 "ios/web/public/payments/payment_request.h"
 
 #include "base/values.h"
 
 namespace {
 
@@ skipping 316 matching lines @@
     const {
   std::unique_ptr<base::DictionaryValue> result(new base::DictionaryValue());
 
   if (!this->method_name.empty())
     result->SetString(kMethodName, this->method_name);
   result->Set(kPaymentDetails, this->details.ToDictionaryValue());
 
   return result;
 }
 
-void PaymentResponse::ToDictionaryValue(base::DictionaryValue* value) const {
-  value->MergeDictionary(ToDictionaryValue().get());
-}
-
 }  // namespace web