I am trying to deactivate Auto-login on the system settings/user accounts, but it even after I reboot the computer it will still log in automatically.
You dont' need your lightdm.conf file. I would rename the file as to make the system believe it isn't there. I only hae pantheon-greeter.conf and users.conf in my /etc/lightdm/ folder, and I don't have auto logins.
Make your /etc/lightdm/pantheon-greeter.conf look like this, too:
I really don't think you need a lightdm.conf for elementary. Try renaming the file.