fdisk: remove Mac code

The code has been used only to detect magic strings, nothing else.

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: remove ugly fatal() function

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: (dos) use ask API to change disk ID

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