bpo-43268: Pass interp rather than tstate to internal functions (GH-24580)

Pass the current interpreter (interp) rather than the current Python
thread state (tstate) to internal functions which only use the
interpreter.

Modified functions:

* _PyXXX_Fini() and _PyXXX_ClearFreeList() functions
* _PyEval_SignalAsyncExc(), make_pending_calls()
* _PySys_GetObject(), sys_set_object(), sys_set_object_id(), sys_set_object_str()
* should_audit(), set_flags_from_config(), make_flags()
* _PyAtExit_Call()
* init_stdio_encoding()
* etc.
diff --git a/Objects/sliceobject.c b/Objects/sliceobject.c
index 02ba033..22fb7c6 100644
--- a/Objects/sliceobject.c
+++ b/Objects/sliceobject.c
@@ -97,9 +97,8 @@ PyObject _Py_EllipsisObject = {
 /* Slice object implementation */
 
 
-void _PySlice_Fini(PyThreadState *tstate)
+void _PySlice_Fini(PyInterpreterState *interp)
 {
-    PyInterpreterState *interp = tstate->interp;
     PySliceObject *obj = interp->slice_cache;
     if (obj != NULL) {
         interp->slice_cache = NULL;