Delete worker activities when using DestroyWorkerResults with a model version

https://redmine.teklia.com/issues/6401

DestroyWorkerResults was implemented back when we only had worker_version_id and configuration_id on worker activities, and not model_version_id. When the model version filter is set, it therefore does not delete any worker activities because it cannot restrict those to the ones with the relevant model version. We do have a model_version_id on worker activities since #1560 (closed), so we can now have the RQ task delete worker activities normally.