[Feature flag] Cleanup member_promotion_management

Summary

This issue is to cleanup the member_promotion_management feature flag, after the feature flag has been enabled by default for Self-Managed Customers in #439113 (comment 2147519968) / !167757 (merged).

This Feature Flag was created to control the release of Add Controls For Ability To Promote Guests for Self-Managed Customers. The Feature will be part of the product now and its available if the application setting enable_member_promotion_management is enabled.

Relevant Docs

Owners

• Team: grouputilization
• Most appropriate slack channel to reach out to: #g_utilization
• Best individual to reach out to: @suraj_tripathy / @sheldonled
• PM: @alex_martin

Stakeholders

N/A

Expectations

What might happen if this goes wrong?

N/A

Cleaning up the feature flag

• Specify in the issue description if this feature will be removed completely or will be productized as part of the Feature Flag cleanup
• Create a merge request to remove member_promotion_management feature flag. Ask for review and merge it.
  • Remove all references to the feature flag from the codebase.
  • Remove the YAML definitions for the feature from the repository.
  • Create a changelog entry.
• Ensure that the cleanup MR has been deployed to both production and canary. If the merge request was deployed before the code cutoff, the feature can be officially announced in a release blog post.
  • /chatops run auto_deploy status <merge-commit-of-cleanup-mr>
• Close the feature epic to indicate the feature will be released in the current milestone.
• If not already done, clean up the feature flag from all environments by running these chatops command in #production channel: /chatops run feature delete member_promotion_management --dev --pre --staging --staging-ref --production
• Close this rollout issue.