Remove CWV class and move setting User Agent to CWVWebViewConfiguration.

ios/web_view/internal/web_view_web_main_delegate.h

Index: ios/web_view/internal/web_view_web_main_delegate.h
diff --git a/ios/web_view/internal/web_view_web_main_delegate.h b/ios/web_view/internal/web_view_web_main_delegate.h
index de7a2d7e92d37ef8dca9027cb6b4840e3d8e6969..ce6baefdcb81d3242e9f75049fe781cd499a5595 100644
--- a/ios/web_view/internal/web_view_web_main_delegate.h
+++ b/ios/web_view/internal/web_view_web_main_delegate.h
@@ -17,16 +17,13 @@ class WebViewWebClient;
 // WebView implementation of WebMainDelegate.
 class WebViewWebMainDelegate : public web::WebMainDelegate {
  public:
-  explicit WebViewWebMainDelegate(const std::string& user_agent_product);
+  WebViewWebMainDelegate();
   ~WebViewWebMainDelegate() override;
 
   // WebMainDelegate implementation.
   void BasicStartupComplete() override;
 
  private:
-  // The name of the product to be used in the User Agent string.
-  std::string user_agent_product_;
-
   // The content and web clients registered by this object.
   std::unique_ptr<WebViewWebClient> web_client_;