[SQL][MINOR] simplify a test to fix the maven tests

## What changes were proposed in this pull request?

After https://github.com/apache/spark/pull/15620 , all of the Maven-based 2.0 Jenkins jobs time out consistently. As I pointed out in https://github.com/apache/spark/pull/15620#discussion_r91829129 , it seems that the regression test is an overkill and may hit constants pool size limitation, which is a known issue and hasn't been fixed yet.

Since #15620 only fix the code size limitation problem, we can simplify the test to avoid hitting constants pool size limitation.

## How was this patch tested?

test only change

Author: Wenchen Fan <wenchen@databricks.com>

Closes #16244 from cloud-fan/minor.