xfs: remove deprecated sysctl options

These optionr were for Irix compatibility, probably for clustered XFS
clients in a heterogenous cluster which contained both Irix & Linux
machines, so that behavior would be consistent. That doesn't exist anymore
and it's no longer needed.

Signed-off-by: Pavel Reichl <preichl@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
[darrick: actually state when the sysctls go away]
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>