nixos/chromium-suid-sandbox: remove reference to grsecurity

nixos/modules/security/chromium-suid-sandbox.nix

···
 
       Also, if the URL chrome://sandbox tells you that "You are not adequately
       sandboxed!", turning this on might resolve the issue.
-
-      Finally, if you have <option>security.grsecurity</option> enabled and you
-      use Chromium, you probably need this.
     '';
   };