[Feature flag] Cleanup hide_deprecated_billing_plans

Summary

This issue is to cleanup the <feature-flag-name> feature flag, after the feature flag has been enabled by default for an appropriate amount of time in production.

Owners

• Team: ~"group::billing and subscription management"
• Most appropriate slack channel to reach out to: #g_billing_and_subscription_management
• Best individual to reach out to: @rhardarson
• PM: @tgolubeva

Stakeholders

Expectations

Bronze and Starter plans are not shown on GitLab Billing page

This feature flag has been on for a while so the functionality should remain the same

What might happen if this goes wrong?

Cleaning up the feature flag

• Create a merge request to remove hide_deprecated_billing_plans 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 issue 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 <feature-flag-name> --dev
  • /chatops run feature delete <feature-flag-name> --staging
  • /chatops run feature delete <feature-flag-name>
• Close this rollout issue.