RFR: 8367601: Remove held_monitor_count

[Fredrik Bredberg]

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.

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Commit messages:
 - 8367601: Remove held_monitor_count

Changes: https://git.openjdk.org/jdk/pull/27570/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27570&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367601
  Stats: 385 lines in 25 files changed: 0 ins; 378 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/27570.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27570/head:pull/27570

PR: https://git.openjdk.org/jdk/pull/27570