Check for boot flag before possibly creating FAT16 on the partition
Checks should be performed before actually modifying the USB device,
if the user specified `--fat16` then the boot flag should be checked
*before* the FAT filesystem gets created.
check_for_fat(device) is called in handle_vfat(device) (if device is
present and not a directory and if option 'syslinux' (default) is set)
so it should be safe to remove check_for_fat(device) call in
install_grml().
The same applies to check_boot_flag() which should happen before
actually creating the FAT filesystem (in handle_vfat()).
Closes: grml/grml2usb#30