Remove lists

There were used originally to semantically a parent with it's children, so a checkbox could have sub-checkboxes. However this is no longer used in any of the facet schemas, and the li/ul add to the noise screen readers make, which isn't needed. So removing these.
Remove sibling support

Since we aren't using this feature and don't plan to start any time soon, remove the ability to have nested checkboxes, and the javascript that keeps the parent checkboxes up to date with their children's checkedness.
Remove updateCheckboxes()

Since all this does is call updateCheckboxResetter() we can removed this too!