lightdm config HELP

[François Patte]

Bonjour,

I have made a great error installing "lightdm-settings" : it is supposed 
to help to configure the startup screenof lightdm...

Not only does it not do what is requested, but it is also impossible to 
get rid of what it has done.

I remove that package and erased the slick-greeter.conf file it has 
written but the ugly config is still there....

How to get totally rid of what it has done?

Thank you.

F.P.