[FF cleanup] Subscription upgrade: use_orders_api_upgrade_workflow

Problem

The scope of this issue is to perform cleanup tasks for FF use_orders_api_upgrade_workflow (original rollout issue).

Proposal

Perform Release the feature tasks:

• Create a merge request to remove <feature-flag-name> feature flag
  • Remove all references to the feature flag from the codebase
• Ensure that the cleanup MR has been deployed to both staging and production
• Disable the feature flag via the CustomersDot dashboard
• Ensure production environment is still working as expected
• Remove the Unleash feature flag from the CustomersDot dashboard
• Close this issue.