/schedules/backup/ include most_recent_task

[rgaudin]

API documentation states that the schedules backup endpoint doesn't include most_recent_task data but it currently does.

• https://api.farm.openzim.org/v1#/public/dumpSchedules
• https://api.farm.openzim.org/v1/schedules/backup/

I believe we chose not to include it because it's task-related and thus transient data while the schedule is the permanent information we want to keep.