Remove extra WKWebView file not used (facebook#21182)

Summary:
This file was created recently but is not used as the WKWebview was integrated directly into the Webview.ios.js

Removing this file to clarify the situation
Pull Request resolved: facebook#21182

Differential Revision: D9942905

Pulled By: hramos

fbshipit-source-id: 19e9fba94280428edd1deab4a54f8c5dc42a6bfa

Author: Titozzz