Fix problems handling 410 and 404 from the content api

This reintroduces code that somehow got lost. If we receive a 404 or a 410 from the content api in `getArticles` of `ParseCollection`, we just continue as normal and it will not be included in the list.

We have been seeing a lot of these error codes from the content API recently due to takedowns.

@ironsidevsquincy