remove zip::unzip

[skeydan]

This PR removes the dependency on zip::unzip added in version 0.4.0.

The problem is that zip::unzip may result in corrupted files. The following was seen on Fedora 37, unzipping the tiny_imagenet dataset:

• The line unzip(raw_path, exdir = self$root_path) creates a path genet-200 (instead of unzipping to the given directory, which in this case is the same as the one the zip file is in)

• Some files are extracted correctly, but in val/val_annotations.txt/, there is nothing.

[skeydan]

Issue in zip::unzip: https://github.com/r-lib/zip/issues/99

[skeydan]

thanks @dfalbel !