In an emergency situation whereby for some reason the Mac Logon Client locks you out of the machine due to an issue, there is a back door to uninstall it, remotely. However thios would have required the administrator to have set up Remote Login, on the Mac device, before hand.
Please refer to the following document for accessing a Mac via SSH with Remote Login: How to Access a Mac via SSH with Remote Login
Even if you are unable to get onto the Mac via the GUI, you will be able to log into it using the steps described with Remote Login.
Once accessed, you use the following Terminal Command:
You will be promoted for your password, and then it will execute the command.
Once completed, restart the Mac. You should be able to log on via the regular Mac logon screen.