RFR: 8369277: Remove unused CodeCacheUnloadingTask::_num_workers [v4]

[Albert Mingkun Yang]

> Trivial removing dead code.
> 
> Test: tier1

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27671/files
  - new: https://git.openjdk.org/jdk/pull/27671/files/be17b8bf..aea09613

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27671&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27671&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27671.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27671/head:pull/27671

PR: https://git.openjdk.org/jdk/pull/27671