RFR: 8367601: Remove held_monitor_count [v2]

[Aleksey Shipilev]

On Wed, 1 Oct 2025 13:35:52 GMT, Fredrik Bredberg <fbredberg at openjdk.org> wrote:

>> Since we have removed all other locking modes than lightweight locking (see: [JDK-8344261](https://bugs.openjdk.org/browse/JDK-8344261)), we no longer need:
>> - `_held_monitor_count`
>> - `_parent_held_monitor_count`
>> - `_jni_monitor_count`
>> 
>> This PR removes them from shared code as well as from `X86`, `AArch64`, `PowerPC` and `RISC-V`.
>> They are not present in other platforms.
>> 
>> Tested tier1-7 (on supported platforms) without seeing any problems that can be traced to this code change.
>> `PowerPC` and `RISC-V` has been sanity checked using QEMU.
>
> Fredrik Bredberg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update after review

Good cleanup, thanks!

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Marked as reviewed by shade (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27570#pullrequestreview-3303476645