Items are added to the collection created for an import as they're
saved, before the imported collection hierarchy exists, so an item only
in a subcollection ended up in the top collection as well as its own.
Remove those once the hierarchy has been created.
When everything imported belongs to a single top-level collection, that
collection is used for the import rather than being nested inside a
collection named after the file.
https://forums.zotero.org/discussion/133174/
This is hard to do currently because the natural place to do it (and
where the previous seeAlso stuff was done) is translate_item.js, but
with async import translators that now only gets one item at a time,
whereas saving item relations requires all items to be saved. So this
would probably need to be done in the import code in translate.js.
It might also require undoing
https://github.com/zotero/zotero/pull/453 so that getResourceURI() works
on notes and figuring out another solution for the problem that was
trying to solve.
