delete method
Implementation
@override
Future<void> delete(String key) async {
var changed = false;
final file = await _recordFile(key);
if (await file.exists()) {
await file.delete();
changed = true;
}
final legacy = _legacyFile(key);
if (legacy != null && await legacy.exists()) {
await legacy.delete();
changed = true;
}
if (changed) notifyListeners(key);
}