Student alumni profiles are listed twice

[thatbudakguy]

Describe the bug
Student alumni who have had multiple roles at the CDH appears to have their profile listed twice in the alumni section — currently Stephanie, Dylan, Kate Carpenter, etc.

Expected behavior
Profiles should only be listed once, and sorted by their most recent role.

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dev notes

Now that we're on postgresql, let's try the distinct on user id (postgres supports specifying a field to use for the distinct)

[kmcelwee]

When distinct('pk') filter is added to the PersonListView or StudentListView's get_queryset methods we get the following error:

annotate() + distinct(fields) is not implemented.

Shifting the order of the method chain did not remove the error.