To remove this option, navigate to: 
  1. Core > Users /Access > Manage Roles
  2. Select Parent of Candidate
  3. Select Tasks
  4. Click Edit
  5. Next to *Official Notes :....Add Official Note, unmark the checkbox 
  6. Click Save & Exit
Note: Log out and log back in to see the changes reflected. It may take a few minutes for you to see the reflected changes.