SQL Server - cannot drop idle job
You have maintenance plans. Try to follow these steps:

Find the maintenance plan name and id that you want to delete.
Write down the id of the one you want to delete.

 SELECT name, id FROM msdb.dbo.sysmaintplan_plans


--Place the id of the maintenance plan you want to delete into the below query to delete the entry from the log table:

    DELETE FROM msdb.dbo.sysmaintplan_log WHERE plan_id = ''


Place the id of the maintenance plan you want to delete into the below query and delete the entry from subplans table:

    DELETE FROM msdb.dbo.sysmaintplan_subplans WHERE plan_id = ''


Place the id of the maintenance plan you want to delete into the below query to delete the entry from the plans table:

    DELETE FROM msdb.dbo.sysmaintplan_plans WHERE id = ''


Now you can delete the jobs from Management Studio.