deleteTrack method
Implementation
@override
Future<void> deleteTrack(String trackId) async {
final track = await getTrack(trackId);
if (track == null) throw StateError('Unknown fake route.');
if (!track.isTerminal) throw StateError('Complete the fake route first.');
_tracks.remove(trackId);
_points.remove(trackId);
_history.add(TrackHistoryEvent(
kind: TrackHistoryChangeKind.deleted, trackId: trackId));
_publish();
}