RFR: 8373272: Genshen: ShenandoahOldGenerationTest fails after JDK-8373056

[Xiaolong Peng]

ShenandoahOldGeneration::configure_plab_for_current_thread has been updated to only handle plab req, which is a behavior change, but ShenandoahOldGenerationTest was not updated to match the behavior change, causing the test to fail.

The two failing unit tests of ShenandoahOldGenerationTest have been removed in this PR since the behavior being verified with them is no longer in configure_plab_for_current_thread, meanwhile one more unit test is added to verify the behavior of `expend_promoted`

### Test
- [x] CONF=macosx-aarch64-server-fastdebug make test TEST=gtest
- [ ] CONF=macosx-aarch64-server-fastdebug make test TEST=hotspot_gc_shenandoah

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Commit messages:
 - Remove tests and revert the changes to configure_plab_for_current_thread
 - Rework on configure_plab_for_current_thread and the unit test to fix test failures

Changes: https://git.openjdk.org/jdk/pull/28706/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28706&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373272
  Stats: 26 lines in 1 file changed: 0 ins; 23 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/28706.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28706/head:pull/28706

PR: https://git.openjdk.org/jdk/pull/28706