xfs: remove xfs_attri_remove_iter

xfs_attri_remove_iter is not used anymore, so remove it and all the
infrastructure it uses and is needed to drive it. THe
xfs_attr_refillstate() function now throws an unused warning, so
isolate the xfs_attr_fillstate()/xfs_attr_refillstate() code pair
with an #if 0 and a comment explaining why we want to keep this code
and restore the optimisation it provides in the near future.

Signed-off-by: Dave Chinner <[email protected]>
Reviewed-by: Allison Henderson<[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Dave Chinner <[email protected]>

Author: Dave Chinner