## What changes were proposed in this pull request?

- Fix tests regarding show functions functionality
- Revert `catalog.ListFunctions` and `SHOW FUNCTIONS` to return to `Spark 1.X` functionality.

Cherry picked changes from this PR: https://github.com/apache/spark/pull/13413/files

## How was this patch tested?

Unit tests.

Author: Bill Chambers <bill@databricks.com>
Author: Bill Chambers <wchambers@ischool.berkeley.edu>

Closes #13916 from anabranch/master.