packages/config/extras: remove all plymouth/wallpaper customizations, use Debian defaults

config/includes.chroot/etc/lightdm/lightdm-gtk-greeter.conf

@@ -45,7 +45,7 @@
 #  transition-duration = overrides default value
 #
 [greeter]
-background = /usr/share/backgrounds/cc0-wallpapers/unsplash10.jpg
+background = /usr/share/desktop-base/futureprototype-theme/wallpaper/contents/images/1600x1200.svg
 user-background = false
 theme-name = Arc-Darker
 icon-theme-name = Papirus