## What changes were proposed in this pull request?

Some PySpark examples need a SparkContext and get it by accessing _sc directly from the session.  These examples should use the provided property `sparkContext` in `SparkSession` instead.

## How was this patch tested?
Ran modified examples

Author: Bryan Cutler <cutlerb@gmail.com>

Closes #13303 from BryanCutler/pyspark-session-sparkContext-MINOR.