xfs: xfs_cluster_write is redundant

xfs: xfs_cluster_write is redundant

xfs_cluster_write() is not necessary now that xfs_vm_writepages()
aggregates writepage calls across a single mapping. This means we no
longer need to do page lookups in xfs_cluster_write, so writeback
only needs to look up th epage cache once per page being written.
This also removes a large amount of mostly duplicate code between
xfs_do_writepage() and xfs_convert_page().

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
(cherry picked from commit ad68972acb82c3e8bba316d542ab204984cb1f1c)

Orabug: 28193043

Signed-off-by: Shan Hai <shan.hai@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>