Remove ufs fragments logic.

The ext2fs fragments are different from ufs fragments.
In case of ext2fs the fragment should be equal or more then block size.
The values more than block size are used only in case of bigalloc feature, which is does not supported for now.

Reported by: Christopher Krah, Thomas Barabosch, and Jan-Niclas Hilgert of Fraunhofer FKIE
Reported as: FS-22-EXT2-9: Denial of service in ftruncate-0 (ext2_balloc)

MFC after: 2 weeks