RFR: 8328341: Remove deprecated per-thread compiler stats in sun.management

[Eirik Bjørsnøs]

Please review this cleanup PR which removes per-thread compiler stats from `sun.management`

This removes:

* The deprecated interface method `HotspotCompilationMBean.getCompilerThreadStats()` along with the implementation method in `HotspotCompilation`
* The class returned by these methods, `CompilerThreadStat`
* The nested class `HotspotCompilation.CompilerThreadInfo` which now falls out of use
* The field `HotspotCompilation.threads`, along with its initialization in `initCompilerCounters`

Testing and verification: As this is purely a removal and cleanup PR of unused code, no updates are made on the testing side. I have verified that the string `getCompilerThreadStats` is not found in OpenJDK after this PR.

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Commit messages:
 - Remove HotspotCompilationMBean.getCompilerThreadStats() with associated implementation code

Changes: https://git.openjdk.org/jdk/pull/18344/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18344&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328341
  Stats: 149 lines in 3 files changed: 0 ins; 147 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18344.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18344/head:pull/18344

PR: https://git.openjdk.org/jdk/pull/18344