Remove deprecated option

Author: sobakintech

docusaurus.config.ts

@@ -26,7 +26,6 @@ const config: Config = {
   projectName: 'usage-guide', // Usually your repo name.
 
   onBrokenLinks: 'throw',
-  onBrokenMarkdownLinks: 'warn',
 
   // Even if you don't use internationalization, you can use this field to set
   // useful metadata like html lang. For example, if your site is Chinese, you