### What changes were proposed in this pull request?

Currently, the Hive built-in `hash` function is not being used in Spark since Spark 2.0. The public interface does not allow users to unregister the Spark built-in functions. Thus, users will never use Hive's built-in `hash` function.

The only exception here is `TestHiveFunctionRegistry`, which allows users to unregister the built-in functions. Thus, we can load Hive's hash function in the test cases. If we disable it, 10+ test cases will fail because the results are different from the Hive golden answer files.

This PR is to remove `hash` from the list of `hiveFunctions` in `HiveSessionCatalog`. It will also remove `TestHiveFunctionRegistry`. This removal makes us easier to remove `TestHiveSessionState` in the future.
### How was this patch tested?
N/A

Author: gatorsmile <gatorsmile@gmail.com>

Closes #14498 from gatorsmile/removeHash.

(cherry picked from commit 57626a55)
Signed-off-by: Reynold Xin <rxin@databricks.com>