gh-105182: Remove PyEval_AcquireLock() and PyEval_InitThreads() (#105183)

Remove functions in the C API:

* PyEval_AcquireLock()
* PyEval_ReleaseLock()
* PyEval_InitThreads()
* PyEval_ThreadsInitialized()

But keep these functions in the stable ABI.

Mention "make regen-limited-abi" in "make regen-all".