Remove update_organization_users feature flag

What does this MR do and why?

Remove update_organization_users feature flag

• rollout was successful on production in #435868 (closed), we can commit to the code now and remove the feature flag

Changelog: other

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #435868 (closed)