deposit: Remove 'parent' deposit
This diff un-reverts !230 (closed).
The parent is computed by the deposit as the revision of the latest deposit in the same origin before the current one. Therefore, it is redundant, as it can be recomputed from metadata
- revision date.
This is a preliminary change needed to make package loaders produce releases instead of revisions, as releases don't have parent relationships
Migrated from D6600 (view on Phabricator)