[SPARK-21604][SQL] if the object extends Logging, i suggest to remove the var LOG which is useless.

## What changes were proposed in this pull request?

if the object extends Logging, i suggest to remove the var LOG which is useless.

## How was this patch tested?

Exist tests

Author: zuotingbing <zuo.tingbing9@zte.com.cn>

Closes #18811 from zuotingbing/SPARK-21604.