The Time Off module no longer keeps an unused manager reference on leave records. This simplifies the underlying data model without changing day-to-day employee or manager workflows.

The `manager_id` field is no longer used in the `hr_leave` model and is therefore removed.

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This change removes old email composer and scheduling fields that are no longer used after a newer approach was introduced. It helps keep the Mail app simpler and easier to maintain without changing current user workflows.

The time off planning view was cleaned up by removing a manager field that is no longer used. This reduces unnecessary configuration in the HR holidays Gantt view without changing the employee-facing time off process.

The `manager_id` field is no longer used in the `hr_leave` model and is therefore removed from the hr_holidays_gantt_view.