xfs: CIL context doesn't need to count iovecs

Now that we account for log opheaders in the log item formatting
code, we don't actually use the aggregated count of log iovecs in
the CIL for anything. Remove it and the tracking code that
calculates it.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chandan Babu R <chandan.babu@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>