Deduplicate arxiv and zbmath papers

[LizzAlice]

There are papers from arxiv that were tagged with the zbmath de number and the zbl id; these should be removed and the paper should be entered as "preprint of" the item imported from zbmath; the description should be adjusted to delete the de number if necessary

[LizzAlice]

Another issue that makes this harder: Some zbmath papers should have the de number in the description but don't
✅✅✅✅✅✅🔲🔲🔲🔲84.5%/100%
(✅🔲)

[LizzAlice]

Some don't have a de number anymore but still have it in the description