If you installed and removed lightdm-kde-greeter and you want to go back to Unity's lightdm try:
sudo dpkg-reconfigure unity-greeter sudo dpkg-reconfigure lightdm
and select lightdm and reboot.
If you installed and removed lightdm-kde-greeter and you want to go back to Unity's lightdm try:
sudo dpkg-reconfigure unity-greeter
sudo dpkg-reconfigure lightdm
and select lightdm and reboot.