Revert problematic background migration and clear it from the Sidekiq queue

This merge request does two things:

1. Reverts !22974 (merged)

2. Clears PatchPrometheusServicesForSharedClusterApplications from the Sidekiq queue.

This job can blow up Sidekiq queues by retrying excessively. Background jobs are intended to process many rows for a large batch of records, but this migration tends to process a single row within a second. As a result, the 2-minute exclusive lease causes this job to rescheduled over and over again.

Identified in https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/9064