FIX: Ascending/descending sorting in the group membership requests page (PR #13761)

The GroupsController#members endpoint accepts a desc parameter to determine how members are sorted, but it’s been deprecated in favor of a boolean asc parameter. However, in the frontend, specifically the group membership requests page was not updated entirely to use the asc param and it still passes a desc param when changing how group requests are sorted.

This PR updates the group-requests Ember controller so it passes a boolean asc param and removes all references of desc. The controller view/template has already been updated to use asc: