remove dead links

Author: righettod

tab_headers.md

@@ -215,7 +215,6 @@ X-Permitted-Cross-Domain-Policies: none
 ### References
 
 * [https://www.adobe.com/devnet-docs/acrobatetk/tools/AppSec/xdomain.html](https://www.adobe.com/devnet-docs/acrobatetk/tools/AppSec/xdomain.html "SKIP_VALIDATION")
-* <https://rorsecurity.info/portfolio/new-http-headers-for-more-security>
 
 ## Referrer-Policy