Only fetch SFU members of maillists for purposes of enrollment syncing
Don't delete populated sections from the current term at all

- Canvas has a bug where if a student is deleted from a section, all
  of their group memberships for the course are also deleted. Therefore,
  if a course moves from a "D100" section structure to a "D101,D102,D103" structure,
  requiring that all students be dropped from D100 and added to D101,D102, etc, their
  group memberships would be lost in the process. As a workaround, we just won't delete
  sections from the current term if they have any student enrollments. The assumption
  is that for future terms, a professor hasn't likely set up group structures yet