remove<P>  method 
- String restorationId
 
Deletes the value currently stored under the provided restorationId from
the bucket.
The value removed from the bucket is casted to P and returned. If no
value was stored under that id, null is returned.
See also:
Implementation
P? remove<P>(String restorationId) {
  assert(_debugAssertNotDisposed());
  final bool needsUpdate = _rawValues.containsKey(restorationId);
  final P? result = _rawValues.remove(restorationId) as P?;
  if (_rawValues.isEmpty) {
    _rawData.remove(_valuesMapKey);
  }
  if (needsUpdate) {
    _markNeedsSerialization();
  }
  return result;
}