Remove PThread.runningWorkers. NFC

[sbc100]

Remove PThread.runningWorkers and use PThread.pthreads instead to track running workers. PThread.pthreads already contains all the necessary information, and keeping both in sync was redundant.

This also optimizes thread exit by replacing an O(N) array splice with an O(1) map deletion, at the cost of making count queries (mostly used in tests) O(N) instead of O(1).

[kleisauke]

Although this API is intended for internal use only, I think we need a changelog entry for this. wasm-vips previously relied on this in an EM_JS block (see e.g. commit kleisauke/wasm-vips@1f8497d where it was removed) and I also noticed that emnapi depends on it as well:
https://github.com/search?q=repo%3Atoyobayashi%2Femnapi%20PThread.runningWorkers&type=code

/cc @toyobayashi FYI.

[sbc100]

Good idea. Added a ChangeLog entry.

[sbc100]

gentle ping @kripken or @kleisauke ?

[kleisauke]

LGTM, but the commit message includes the following trailers:

TAG=agy
CONV=47f918e2-bd47-4e38-9a6d-af1765cf2f7e

I'm not sure whether these were added intentionally or what they are meant to indicate.

[kleisauke]

TIL, https://github.com/v8/v8/blob/15.0.218/agents/rules/git-commit.md?plain=1#L23-L24.

[sbc100]

LGTM, but the commit message includes the following trailers:

TAG=agy
CONV=47f918e2-bd47-4e38-9a6d-af1765cf2f7e

I'm not sure whether these were added intentionally or what they are meant to indicate.

They were not supposed to be there. Luckily the final commit message used is based on the PR description and not the git commit messages, and they were already removed therre.