Stop creating tasks directly in listers

Once the new lister tables are used to schedule recurrent visits, we should stop having listers generate recurrent tasks themselves.

---

Migrated from T2454 (view on Phabricator)

assigned to @olasd

marked this issue as related to #2453 (closed)

marked this issue as related to swh-scheduler#2444

added Lister priority:Normal labels

This has all landed during the early 2021 sprint.

unassigned @olasd

closed