Clean the path the same way on all platforms

[triple-j]

I was testing --human-folders on Linux and ran into an issue where game names that contain a forward slash (/) would be broken up into multiple folders. So I removed the platform check in clean_path().

This is also better for compatibility. It's rare, but this allows someone to move their folders to different platforms. Since the files/folders are now created the same on all platform, the user won't accidentally re-download files if they run this project on multiple platforms.