[MINOR][SQL][TEST] no uncache table in joinsuite test

## What changes were proposed in this pull request?

At present, in test("broadcasted hash outer join operator selection") case,  set the testData2 to _CACHE TABLE_, but no _uncache table_ testData2. It can make people confused.
In addition, in the joinsuite test cases, clear the cache table of work by SharedSQLContext _spark.sharedState.cacheManager.clearCache_ to do, so we do not need to uncache table
let's fix it. thanks.

## How was this patch tested?
Existing test cases.

Author: caoxuewen <cao.xuewen@zte.com.cn>

Closes #18914 from heary-cao/uncache_table.