Remove execution-related fields from CampaignJobs
Created by: mrnugget
This removes all the fields on CampaignJob that are not used anymore:
- FinishedAt
- StartedAt
- Error
- Description
With #8008 those became useless.
What this does is remove the fields but leave the GraphQL API intact. That means we can freely merge it without breaking anything.
The changes in #9068 will need to be rebased on this here.