[SPARK-19810][SPARK-19810][MINOR][FOLLOW-UP] Follow-ups from to remove Scala 2.10

## What changes were proposed in this pull request?

Follow up to a few comments on https://github.com/apache/spark/pull/17150#issuecomment-315020196 that couldn't be addressed before it was merged.

## How was this patch tested?

Existing tests.

Author: Sean Owen <sowen@cloudera.com>

Closes #18646 from srowen/SPARK-19810.2.