fdisk: use  libfdisk to ask for partition type

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: remove old code to ask user

Old code has been broken by design:

 * use global variables
 * fixed buffer size
 * useless within libfdisk

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: move get_nr_sects() fdisk.h

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: cleanup usage()

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: don't use ptes[] in generic code

... the array is MBR specific.

Signed-off-by: Karel Zak <kzak@redhat.com>