Remove the following private undocumented functions from the C API:

* ``_PyEval_GetAsyncGenFirstiter()``
* ``_PyEval_GetAsyncGenFinalizer()``
* ``_PyEval_SetAsyncGenFirstiter()``
* ``_PyEval_SetAsyncGenFinalizer()``

Call the public :func:`sys.get_asyncgen_hooks` and
:func:`sys.set_asyncgen_hooks` functions instead. Patch by Victor Stinner.
