Avoid adding P1433 = unknown

[dpriskorn]

We discussed in WikiCite https://t.me/c/1497612692/2638

I don't think there is any real justification for not linking directly to the publication using P1433. Sources such as CrossRef and PubMed provide P236 and these can be used to map to Wikidata items for publications. ISSNs will also often be in people's Zotero libraries. Not link P1433 to Wikidata items makes work for others, and potentially impacts our ability to avoid adding duplicate references for articles that lack well known identifiers such as P356.