xfs: don't implement XFS_IOC_RESVSP / XFS_IOC_RESVSP64

These ioctls are implemented by the VFS and mapped to ->fallocate now,
so this code won't ever be reached.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>