The type of event raised after an item has been removed from a collection.
The event will be raised at a point of time, where the collection object is
in an internally consistent state and before the corresponding CollectionChanged
event is raised.
Note: The Clear() operation will not fire ItemsRemoved events.
Note: an Update operation will fire an ItemsRemoved and an ItemsAdded event.
Note: When an item is removed from a list by the RemoveAt operation, both an
ItemsRemoved and an ItemRemovedAt event will be fired.