With newer Windows 10 versions, `install.wim` can become larger than
4GiB, which can't be placed in a FAT32 partition anymore. By splitting
it into chunks with `wimsplit` and removing `install.wim`, the larger
images work fine.
Since we set RTC in the Nix build it's likely that any passwords have
expired since the image generation RTC time.
Ideally this should be applied in autounattend.xml but it didn't work
out either as FirstLogonCommands or as a command in the specialize pass.