Update backend.py

[danielcamposramos]

Changed the Models list.

[pluja]

Why did you remove the tiny, small, base, medium, etc?...

[danielcamposramos]

It seemed more streamlined to keep only the most recent versions...do as you wish, master; they are still there (you might just add the newer ones).

[pluja]

There are devices that are not able to run large models, so I think it'd be better to keep them all