## What changes were proposed in this pull request?

Remove all usages of Scala Tuple2 from common/network-* projects. Otherwise, Yarn users cannot use `spark.reducer.maxReqSizeShuffleToMem`.

## How was this patch tested?

Jenkins.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #18593 from zsxwing/SPARK-21369.