After you create the popcorn event, you need to retrieve the id that Popcorn generated, like this:
var id = popcorn.getLastTrackEventId();
In practice, you'd probably put it into an array so you can store an id for all your events. Then, to delete it:
popcorn.removeTrackEvent(id);
_teardown
gets called automatically by removeTrackEvent
along with other clean-up work that it does.