[XFS] Remove xfs_physmem

Now that nobody's using it, remove xfs_physmem & friends.

SGI-PV: 968563
SGI-Modid: xfs-linux-melb:xfs-kern:29325a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>