Release jira_connect_remove_branches

What does this MR do and why?

This removes the :jira_connect_remove_branches feature flag as the feature has been globally enabled on production for a week with no issues.

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 #456457 (closed)