Re-enable USBs check in wsl `SetProviderAttrs` function to prevent the
user trying to set USB settings which isn't supported.
Additionally removes a TODO in wsl's `CreateVM` function to check if the
`opts.USBs` length is greater than 0. This check is done in a more
generic way higher up the stack.
Signed-off-by: Jake Correnti <jakecorrenti+github@proton.me>