UBIFS: remove dead code

Remove dead pieces of code under "if (c->min_io_size == 1)" statement -
we never execute it because in UBIFS 'c->min_io_size' is always at least 8.
This are leftovers from old pre-mainline prototype.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>