Comment 3 for bug 1109338

From the terminal log:

Purging configuration files for lightdm ...
Removing user `lightdm' ...
Warning: group `lightdm' has no more members.
userdel: user lightdm is currently logged in
/usr/sbin/deluser: `/usr/sbin/userdel lightdm' returned error code 8. Exiting.
dpkg: error processing lightdm (--purge):
 subprocess installed post-removal script returned error exit status 1

Which indicates that LightDM was probably removed while it was running.

We should probably just warn if this occurs with the penalty that a lightdm user will be left on the system.