clean scaffold lua API

[cderv]

We have two functions, one of them adding the "hidden" class - but we are unsure of why

quarto-cli/src/resources/filters/ast/customnodes.lua

Lines 522 to 538 in e1b9356

	-- wrap an element with another element containing the quarto-scaffold class
	-- so that it will be stripped out in the final output
	scaffold_element = function(node)
	local pt = pandoc.utils.type(node)
	if pt == "Blocks" then
	return pandoc.Div(node, {"", {"quarto-scaffold"}})
	elseif pt == "Inlines" then
	return pandoc.Span(node, {"", {"quarto-scaffold"}})
	else
	return node
	end
	end,
	-- a slightly different version of scaffold_element; we should probably unify these
	make_scaffold = function(ctor, node)
	return ctor(node or {}, pandoc.Attr("", {"quarto-scaffold", "hidden"}, {}))
	end,

And also we still have global function

quarto-cli/src/resources/filters/quarto-finalize/descaffold.lua

Lines 25 to 27 in e1b9356

	function make_scaffold(ctor, node)
	return ctor(node or {}, pandoc.Attr("", {"quarto-scaffold", "hidden"}, {}))
	end

Used only once at

quarto-cli/src/resources/filters/customnodes/theorem.lua

Line 167 in e1b9356

local callthm = make_scaffold(pandoc.Div, preamble)