[docs] remove duplicate entry from 1.13 release notes

Removed a note that was duplicate to the following one:

  * The Spark KuduContext accumulator metrics now track operation
    counts per table instead of cumulatively for all tables.

Change-Id: I186f7160d71e94ed54c0e583655e67e2c0486ae9
Reviewed-on: http://gerrit.cloudera.org:8080/16430
Tested-by: Kudu Jenkins
Reviewed-by: Attila Bukor <abukor@apache.org>
1 file changed