ToDo's alert remains active after its deletion

[Andrew]

After setting an alert for a todo, then deleting the todo, the alert still remains pending and shows at the time specified.

Steps to recreate:

1. Click "New Item"
2. Fill in all fields, setting alert time to 1min in future toggle the Alert? to enabled
3. Save
4. Swipe to delete todo from main list
5. Notification still shows on lock screen and in Notification Center