chore(security): remove redundant heading

Author: naomiblack

public/docs/ts/latest/guide/security.jade

@@ -1,7 +1,6 @@
 block includes
   include ../_util-fns
 :marked
-  # Security
   Web application security has many aspects. This documentation describes Angular's built in
   protections against common web application vulnerabilities and attacks, such as Cross Site
   Scripting Attacks. It does not cover application level security, such as authentication (_Who is