🔥(backend) remove unused order parameter in Paginator class

In the custom Paginator present in the viewset, an ordering parameter
was set. This parameter is never used by the DRF paginator and can be
removed.

src/backend/core/api/viewsets.py

@@ -173,7 +173,6 @@ class SerializerPerActionMixin:
 class Pagination(drf.pagination.PageNumberPagination):
     """Pagination to display no more than 100 objects per page sorted by creation date."""
 
-    ordering = "-created_on"
     max_page_size = 200
     page_size_query_param = "page_size"