bpo-39372: Clean header files of declared interfaces with no implementations (GH-18037)

The public API symbols being removed are:

_PyBytes_InsertThousandsGroupingLocale, _PyBytes_InsertThousandsGrouping, _Py_InitializeFromArgs, _Py_InitializeFromWideArgs, _PyFloat_Repr, _PyFloat_Digits,
_PyFloat_DigitsInit, PyFrame_ExtendStack, _PyAIterWrapper_Type, PyNullImporter_Type, PyCmpWrapper_Type, PySortWrapper_Type, PyNoArgsFunction.

Include/methodobject.h

@@ -22,8 +22,6 @@ typedef PyObject *(*PyCFunctionWithKeywords)(PyObject *, PyObject *,
 typedef PyObject *(*_PyCFunctionFastWithKeywords) (PyObject *,
                                                    PyObject *const *, Py_ssize_t,
                                                    PyObject *);
-typedef PyObject *(*PyNoArgsFunction)(PyObject *);
-
 PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
 PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);
 PyAPI_FUNC(int) PyCFunction_GetFlags(PyObject *);