Update AdminSecurityController.php

Hello,

I was working on a custom login page and came to compare this login Controller with the latest of FOSUserBundle. This one could be updated to follow FOSUserBundle?
https://github.com/FriendsOfSymfony/FOSUserBundle/commit/20b97f61ede32b37266cb3febf2372f82647b617
https://github.com/FriendsOfSymfony/FOSUserBundle/commit/63e308cad922185fc1dedc9f95e92b23fd1c94b1

I removed renderLogin because it seems to no longer have any use to split between 2 methods (correct me if I am wrong ^^) https://github.com/FriendsOfSymfony/FOSUserBundle/blob/master/Controller/SecurityController.php

Also, what is the use of admin_pool ? It's only defined here and not used anywhere in the SonataUserBundle ?