chore: Use preferred collection method delete_one (#34214)

`remove` method of Collection objects has been deprecated in favour
of either `delete_one` or `delete_many`.

This change will address 36 deprecation warnings that are generated from
test runs.

Co-authored-by: Lewis Kabui <[email protected]>

xmodule/modulestore/split_mongo/mongo_connection.py

@@ -506,7 +506,7 @@ def delete_course_index(self, course_key):
                 key_attr: getattr(course_key, key_attr)
                 for key_attr in ('org', 'course', 'run')
             }
-            return self.course_index.remove(query)
+            return self.course_index.delete_one(query)
 
     def get_definition(self, key, course_context=None):
         """