Tests: revisit test decisions for instructor permissions once the UI is more mature

[alex-kozin]

There were several instructor permission tests deleted. They were testing querying Ddahs by assignment id and by position id. It was decided best to delete these tests until the UI is more developed to see if they will be useful at all.

The reasoning was that the admin view currently fetches everything on a per-session basis and later on additional filters may be applied. If instructor view follows the same pattern - we would have no need to query Ddahs on a per-position or per-assignment basis.

The goal of this issue is to revisit this decision when the instructor UI is built out to see if we need these tests (and corresponding functionality) or not.