[SPARK-45305][SQL][TESTS] Remove JDK 8 workaround added TreeNodeSuite

[HyukjinKwon]

What changes were proposed in this pull request?

In theory, we don't need #29875 anymore because we dropped JDK 8 (according to the PR description in #29875) but Utils.getSimpleClass handles malformed class names in any event, so should be safe to keep them.

Why are the changes needed?

To remove test that does not run. We dropped JDK 11/8 at SPARK-44112

Does this PR introduce any user-facing change?

No, test-only.

How was this patch tested?

CI in this PR should test them out.

Was this patch authored or co-authored using generative AI tooling?

No.

[HyukjinKwon]

cc @rednaxelafx

[dongjoon-hyun]

+1, LGTM.

[dongjoon-hyun]

I verified manually this removal. This suite works fine without any compilation issue.

$ build/sbt "catalyst/testOnly *.TreeNodeSuite"
...
[info] Run completed in 1 second, 730 milliseconds.
[info] Total number of tests run: 34
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 34, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[success] Total time: 10 s, completed Sep 25, 2023, 10:07:21 AM

[dongjoon-hyun]

Merged to master.