Remove duplicate url key in Docusaurus siteConfig (facebook#6690)

`url` was duplicated in `siteConfig.js`, both were the same value, so stripping one of them.

Author: charpeni

docusaurus/website/siteConfig.js

@@ -11,7 +11,6 @@
 const siteConfig = {
   title: 'Create React App', // Title for your website.
   tagline: 'Set up a modern web app by running one command.',
-  url: 'https://facebook.github.io', // Your website URL
   // For github.io type URLs, you would set the url and baseUrl like:
   url: 'https://facebook.github.io',
   baseUrl: '/create-react-app/',