delete method
deletes from storage according to LocalValue.basePath and LocalValue.documentType, returning true
if an object existed at the path and was deleted from storage and false otherwise.
It is possible to put a path in id (i.e. write('my/path/${user.id}')),
but is not recommended because subsequent lookups will need to be pathed the same. instead, put
path segments when constructing this LocalValue.
Implementation
Future<bool> delete(String id) {
return super.deleteValue(id);
}