Remove CWV class and move setting User Agent to CWVWebViewConfiguration.

ios/web_view/internal/web_view_web_main_delegate.mm

Index: ios/web_view/internal/web_view_web_main_delegate.mm
diff --git a/ios/web_view/internal/web_view_web_main_delegate.mm b/ios/web_view/internal/web_view_web_main_delegate.mm
index 3160919d3a5f6fd248935e67be21cdc27752f5bd..9841cb6587bd0f7e3eee9c0cbe4527f62fc667d3 100644
--- a/ios/web_view/internal/web_view_web_main_delegate.mm
+++ b/ios/web_view/internal/web_view_web_main_delegate.mm
@@ -15,16 +15,14 @@
 
 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_client_ = base::MakeUnique<WebViewWebClient>();
   web::SetWebClient(web_client_.get());
 }