torch._six is depreciated, remove import

[miamannionx]

Torch does not support torch._six anymore, so removed from torch._six import string_classes

Replaced string_classes with str.

Reference: https://github.com/pytorch/pytorch/pull/94709

[wyardley]

I think this would also resolve #223

[wyardley]

@rromb @manolo-lolo is this project still maintained, and do you know who a current maintainer is?

[manolo-lolo]

@wyardley My guess is that this project is no longer maintained in favor of newer methods/repositories, such as the stable diffusion one. I think @rromb can tell you more.