Open a terminal.
Run the following commands:
sudo -i # to have root privileges
gedit /etc/lightdm/lightdm.conf # to edit /etc/lightdm/lightdm.conf
Add this line to the end of the file:
greeter-show-remote-login=false
Save the file and close it.
Restart lightdm service
(from tty1 with sudo service lightdm restart)
or restart computer.