RFR: 8340119: Remove oopDesc::size_might_change()

[Thomas Schatzl]

Hi all,

  please review this change that removes `oopDesc::size_might_change()` because since JDK-8337709 and JDK-8311163 no collector uses the objArray's length field during garbage collection any more.

Testing: tier1-3

Thanks,
  Thomas

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Commit messages:
 - Hi all,

Changes: https://git.openjdk.org/jdk/pull/20999/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20999&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340119
  Stats: 14 lines in 3 files changed: 0 ins; 13 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20999.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20999/head:pull/20999

PR: https://git.openjdk.org/jdk/pull/20999