xfs: don't need dirv2 checks anymore

If the the V2 directory feature bit is not set in the superblock
feature mask the filesystem will fail the good version check.
Hence we don't need any other version checking on the dir2 feature
bit in the code as the filesystem will not mount without it set.
Remove the checking code.

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