delete method

Implementation

bool delete(int id) {
  final extmark = _extmarks.remove(id);
  if (extmark == null) {
    return false;
  }
  final ids = _extmarksByType[extmark.type];
  ids?.remove(id);
  if (ids != null && ids.isEmpty) {
    _extmarksByType.remove(extmark.type);
  }
  return true;
}