Cleanup Node::query_selector.
Cleanup Node::summarize.
Cleanup Node::clone.
Cleanup Node::ChildNodes.
Cleanup Node::Normalize.
Cleanup Node::CloneNode.
Cleanup Node::as_element.
Cleanup Node::is_html_element_in_html_document.
auto merge of #4280 : Ms2ger/servo/cleanup-node, r=jdm