Refactor finalize new_version method for better performance

[rochacbruno]

Comment from @mdellweg

this can significantly slow down sync, as this collection version basically jumps the whole pipeline without waiting to be processed in batches. We should refactor this soon.

Originally posted by @mdellweg in #1326 (comment)

Also

All we care for in the c_version is the pk. Right? I don't think we need to cast for that. And at that point we don't even need the loop anymore, right?
Would the following work?

    signatures = new_version.get_content(
        content_qs=CollectionVersionSignature.objects.filter(signed_collection__in=removed_collection_versions)
    )
    new_version.remove_content(signatures)

Member

@mdellweg mdellweg 9 hours ago
Also do we maybe need to call remove_duplicates first? It may remove more CVs.