Formally mark deprecated items in threading for removal in 3.21

Feature or enhancement

Proposal:

Several camelCase names in the threading module have been marked with DeprecationWarnings since 3.10. (they are replaced by snake_case names and in some cases with properties rather than getter/setter functions) However, they have never had a removal version set.

I propose to mark these for removal in 3.21 and will prepare a PR to do so.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-154206

首先检查 threading 模块现有的 DeprecationWarnings 以及关联的 PR gh-154206。确认哪些 camelCase 名称缺少移除版本；当相关弃用项都一致声明将在 Python 3.21 中移除时即完成。