[KYUUBI #4834] [MINOR] Reduce the scope of method references in Authz plugin cleanup shutdown hook

### _Why are the changes needed?_

Reduce the scope of method references

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [ ] [Run test](https://kyuubi.readthedocs.io/en/master/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #4834 from wForget/minor.

Closes #4834

2061dc942 [wforget] [MINOR] Reduce the scope of method references

Authored-by: wforget <643348094@qq.com>
Signed-off-by: liangbowen <liangbowen@gf.com.cn>

extensions/spark/kyuubi-spark-authz/src/main/scala/org/apache/kyuubi/plugin/spark/authz/ranger/SparkRangerAdminPlugin.scala

@@ -79,7 +79,7 @@ object SparkRangerAdminPlugin extends RangerBasePlugin("spark", "sparkSql")
       () => {
         if (plugin != null) {
           LOG.info(s"clean up ranger plugin, appId: ${plugin.getAppId}")
-          this.cleanup()
+          plugin.cleanup()
         }
       },
       Integer.MAX_VALUE)