xfsprogs: remove non-Linux defintions for loff_t

We don't use loff_t anywhere in xfsprogs, so no need to define it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>