libblkid: remove workaround for FAT+MBR on whole-disk

libblkid: remove workaround for FAT+MBR on whole-disk

The current libblkid ignores FAT when created on the same whole-disk
device as valid MBR. This restriction is not compatible with many
devices (like USB flash disk) created by Windows or the latest
dosfstools where the first partition is used for entire device and
where is also valid FAT. The filesystem is accessible from partition
as well as from whole-disk device.

The conclusion (between util-linux, dosfstools and udisks) is that
libblkid has to provide all details, not hide anything and the proper
policy (hide/show) has to be implemented by udisks (or so).

CC: Tomáš Bžatek <tbzatek@redhat.com>
CC: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>