remove: remove dvc.yaml and dvc.lock if they are empty

[efiop]

#4074 (comment)

$ cat dvc.lock
{}                                               
$ cat dvc.yaml
stages: {}                                       

[nik123]

The implementaiton of it seems quite straightforward. May I pick it up?

[efiop]

@nik123 Sure! Thank you so much for looking into it! 🙏