delete method
Deletes the document referred to by this DocumentReference.
A delete for a non-existing document is treated as a success (unless
precondition
is specified).
Implementation
Future<WriteResult> delete([Precondition? precondition]) async {
final writeBatch = WriteBatch._(this.firestore)
..delete(this, precondition: precondition);
final results = await writeBatch.commit();
return results.single;
}