RFR: 8367601: Remove held_monitor_count [v2]

[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.

Fredrik Bredberg has updated the pull request incrementally with one additional commit since the last revision:

  Update after review

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/27570/files
  - new: https://git.openjdk.org/jdk/pull/27570/files/f05981b1..a3f09e85

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27570&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27570&range=00-01

  Stats: 16 lines in 4 files changed: 0 ins; 6 del; 10 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