Optimize ListElementLinks

It gives 500 errors in prod on relatively simple transcriptions: https://arkindex.teklia.com/api/v1/element/e3547ffb-7f61-4f28-a76e-86f52fa69125/links/

added 1 deleted label

mentioned in merge request !1187 (merged)

closed

mentioned in commit 148adffc

Sentry issue: ARKINDEX-FRONTEND-6W7