ReferringRelatedDocsProvider never returns any results

The ReferringRelatedDocsProvider should suggest related documents that are referring back. However, it never returns any results, probably because the xpath query it uses contains the UUID of the edited document in draft mode. Since no other document will ever include this draft document as a related document, the query never returns any results.

Steps to reproduce:
1. disable the SimilaritySearchRelatedDocsProvider (not really need, but you can better see the results of the other provider that way)
2. create a document type with a relateddocs field in it
3. create two documents of that type, say A and B
4. let A include B as a related document
5. edit B and check the related documents suggestions

Expected behavior: document A is suggested as a related document (by the ReferringRelatedDocsProvider)
Actual behavior: no related documents are suggested at all