Remove needless check for comment node type.
Remove needless check for comment node type.

Unless "#comment" is added to the allowed types, it won't be kept anyway. And
if someone did want to keep comments, they could now add this to the allowed
tags list.

tdeekens/DOMPurify,neilj/DOMPurify,Joris-van-der-Wel/DOMPurify,voku/DOMPurify,Joris-van-der-Wel/DOMPurify,neilj/DOMPurify,tdeekens/DOMPurify,kwangkim/DOMPurify,voku/DOMPurify,Joris-van-der-Wel/DOMPurify,togusafish/t-ashula-_-DOMPurify,togusafish/t-ashula-_-DOMPurify,ConradIrwin/DOMPurify,neilj/DOMPurify,kwangkim/DOMPurify,tdeekens/DOMPurify,ConradIrwin/DOMPurify