xfs/078: remove the 512 byte block size sub-case

xfs/078: remove the 512 byte block size sub-case

512 byte block sizes are only supported for v4 file systems, and
xfs/078 crudely forces use of v4 file systems for it.  This doesn't
work if the kernel is built without v4 support.  Given that v4
support is slowly being phased out and 512 byte block sizes have never
been common, drop this part of the test.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>