netinfo_to_netplan: /init: 771: /init: rm: not found

[Benjamin Drung]

The qemu-net autopkgtest shows this error message:

```
/init: 778: /init: rm: not found
```

This comes from the `netinfo_to_netplan` function in `scripts/functions`:

```
netinfo_to_netplan() {
[...]
 rm -Rf "$tmpd"
}
```

The `rm` command is only available if busybox is used.