The jdk.vm.ci.hotspot.HotSpotJDKReflection#oopSizeOffset field[1] exists purely to satisfy an libgraal substitution[2]. The latter is unused and is being removed. As such HotSpotJDKReflection#oopSizeOffset can be removed.

[1] https://github.com/openjdk/jdk/blob/45c4eaa5600016d3da5ca769b2519df53835e4f7/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotJDKReflection.java#L112
[2] https://github.com/oracle/graal/blob/940934ae7e0d3b86a9122d5b00bc2789c476a996/substratevm/src/com.oracle.svm.graal.hotspot.libgraal/src/com/oracle/svm/graal/hotspot/libgraal/LibGraalSubstitutions.java#L74