Restoring the default login screen background in Ubuntu Xenial

Changing the desktop wallpaper also changed the login screen. Follow these steps to override that behavior and reset the login screen back to the default.
cd /usr/share/glib-2.0/schemas/
sudo vi com.canonical.unity-greeter.gschema.xml
Look for this key node:
<key name="draw-user-backgrounds" type="b">
<summary>Whether to draw user backgrounds</summary>
Change the value true to false.

You can also remove the white dots by changing this key node:
<key name="draw-grid" type="b">
<summary>Whether to draw an overlay grid</summary>
Now recompile the schema with this command:
sudo glib-compile-schemas /usr/share/glib-2.0/schemas/
Log out and back in to see the change.