[HOTFIX][BUILD] Fix finalizer checkstyle error and re-disable checkstyle

## What changes were proposed in this pull request?

Fix finalizer checkstyle violation by just turning it off; re-disable checkstyle as it won't be run by SBT PR builder. See https://github.com/apache/spark/pull/18887#issuecomment-332580700

## How was this patch tested?

`./dev/lint-java` runs successfully

Author: Sean Owen <sowen@cloudera.com>

Closes #19371 from srowen/HotfixFinalizerCheckstlye.