RFR: 8369483: Cleanup dead code in HandleArea

[Joel Sikström]

Hello,

When reading up on how HandleArea and HandleMark's work, I found some dead code and comments in the HandleArea class. This makes the code a bit easier to read and understand.

Testing:
* Oracles tier1-2

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Commit messages:
 - 8369483: Cleanup dead code in HandleArea

Changes: https://git.openjdk.org/jdk/pull/27717/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27717&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369483
  Stats: 15 lines in 3 files changed: 1 ins; 8 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/27717.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27717/head:pull/27717

PR: https://git.openjdk.org/jdk/pull/27717