repair: remove custom dir2 sf fork verifier from phase6

repair: remove custom dir2 sf fork verifier from phase6

The custom verifier exists to catch the case of repair setting a
dummy parent value of zero on directory inodes and temporarily
replace it with a valid inode number so the rest of the directory
verification can proceed. The custom verifier is no longer needed
now that the rootino is used as a dummy value for invalid on-disk
parent values.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>