ignore_malloc_size_of in NodeIterator and HTMLCollection points at closed issue #6870

[pshaughn]

Since #6870 was resolved I tried taking out the ignore_malloc_size_of lines here, but we still seem to need them. I might not understand what's really happening here, but it looks like the NodeIterator one involves an Rc<NodeFilterBinding::NodeFilter>, which seems like the kind of thing 6870 was supposed to fix. The HTMLCollection one involves a Box<dyn CollectionFilter + 'static> which seems like it probably has to stay ignore_malloc_size_of since the CollectionFilter trait could be hiding anything as far as the compiler knows. The sensible thing to do in the latter case might just be to clean up the comment and leave the ignore on, but the former could point at something to fix in the macros.