No, lightdm-slick-greeter has never been installed on my EOS install. I started out with EOS using Openbox and Tint2, but recently decided to switch to XFCE.
No, /etc/lightdm/lightdm.conf.d/10-eos-slick.conf does not exist. I have /etc/lightdm/lightdm.conf.d/10-eos-gtk.conf.