[XFS] kill struct bhv_vnode

Now that struct bhv_vnode is empty we can just kill it. Retain bhv_vnode_t
as a typedef for struct inode for the time being until all the fallout is
cleaned up.

SGI-PV: 969608
SGI-Modid: xfs-linux-melb:xfs-kern:29500a

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