[XFS] call common xfs vfs-level helpers directly and remove vfs operations

Also remove the now dead behavior code.

SGI-PV: 969608
SGI-Modid: xfs-linux-melb:xfs-kern:29505a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>