Remove split_refresh_worker_pipeline feature flag
What does this MR do?
Removes the split_refresh_worker_pipeline feature flag as it has been fully rolled out and is stable.
Changes
- Remove feature flag YAML definition
- Remove feature flag checks from RefreshService
- Remove old inline pipeline refresh code path
- Update specs to remove feature flag stubbing and legacy tests
- Pipeline creation now always happens asynchronously via PipelineWorker
Edited by Marc Shaw