Omit previous error from Sidekiq JSON logs

What does this MR do?

Sidekiq stores a job's error details in the payload for the next run, so that it can display the error in the Sidekiq UI. This is because Sidekiq's main state is the queue of jobs to be run. However, in our logs, this is very confusing, because we shouldn't have any error at all when a job starts, and we already add an error message and class to our logs when a job fails.

Part of https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/9198.