In order to remove pam-face-authentication from your system, just do the steps in following order. First you have to deselect the plugin, then remove the PAM config file and lastly the package itself.
1. First you have to deselect the plugin
sudo pam-auth-update –package face_authentication
2. then remove the PAM config file
sudo rm /usr/share/pam-configs/face-authentication
3. lastly remove the package itself
sudo apt-get remove pam-face-authentication
That’s all. Now you can login with your password.