Remove CWV class and move setting User Agent to CWVWebViewConfiguration.

ios/web_view/internal/web_view_web_main_delegate.mm

 // Copyright 2014 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.
 
 #import "ios/web_view/internal/web_view_web_main_delegate.h"
 
 #import "base/mac/bundle_locations.h"
-#include "base/memory/ptr_util.h"
-#import "ios/web_view/internal/web_view_web_client.h"
 #import "ios/web_view/public/cwv_web_view.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace ios_web_view {
 
-WebViewWebMainDelegate::WebViewWebMainDelegate(
-    const std::string& user_agent_product)
-    : user_agent_product_(user_agent_product) {}
+WebViewWebMainDelegate::WebViewWebMainDelegate() {}
 
 WebViewWebMainDelegate::~WebViewWebMainDelegate() = default;
 
 void WebViewWebMainDelegate::BasicStartupComplete() {
   base::mac::SetOverrideFrameworkBundle(
       [NSBundle bundleForClass:[CWVWebView class]]);
-  web_client_ = base::MakeUnique<WebViewWebClient>(user_agent_product_);
-  web::SetWebClient(web_client_.get());
 }
 
 }  // namespace ios_web_view