Looks to me like you need :
siduction-settings-lightdm-gtk-december installed .
from apt-cache show siduction-settings-lightdm-gtk-december :
Breaks: siduction-lightdm-settings, siduction-settings-lightdm-december
Replaces: siduction-lightdm-settings, siduction-settings-lightdm-december
Looks safe to purge siduction-settings-lightdm-december
I do not have it installed now