RFR: 8335357: delete HotSpotJDKReflection.oopSizeOffset

[Gergö Barany]

The jdk.vm.ci.hotspot.HotSpotJDKReflection#oopSizeOffset field exists purely to satisfy a libgraal substitution. The latter is unused and is being removed from Graal in https://github.com/oracle/graal/pull/9217. As such HotSpotJDKReflection#oopSizeOffset can be removed.

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Commit messages:
 - 8335357: delete HotSpotJDKReflection.oopSizeOffset

Changes: https://git.openjdk.org/jdk/pull/19966/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19966&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335357
  Stats: 4 lines in 1 file changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19966.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19966/head:pull/19966

PR: https://git.openjdk.org/jdk/pull/19966