datacite importer duplicated author names

Sometimes Datacite metadata includes the same people/entities as both "creators" and "contributors", and we end up duplicating them in fatcat metadata. Eg:

• https://fatcat.wiki/release/spjysmrnsrgyzgq6ise5o44rlu/contribs
• https://api.datacite.org/dois/10.25940/roper-31098406

I think the behavior should probably be to only add the contributors if they are not already in the author list by string check. Not sure if this should be a fuzzy string check; and exact check is a good start.

Will need to do cleanup as well.