Issue #23685: Fix usage of PyMODINIT_FUNC in _json, _scproxy, nis, pyexpat

_codecs_cn, _codecs_hk, _codecs_iso2022, _codecs_jp, _codecs_kr and _codecs_tw
modules.

pyexpat.c doesn't need to redeclare PyMODINIT_FUNC, it's already declared in
Include/pyport.h.

Modules/_json.c

@@ -1995,7 +1995,7 @@ static struct PyModuleDef jsonmodule = {
         NULL
 };
 
-PyObject*
+PyMODINIT_FUNC
 PyInit__json(void)
 {
     PyObject *m = PyModule_Create(&jsonmodule);

Modules/_scproxy.c

@@ -249,7 +249,7 @@ static struct PyModuleDef mod_module = {
 extern "C" {
 #endif
 
-PyObject*
+PyMODINIT_FUNC
 PyInit__scproxy(void)
 {
     return PyModule_Create(&mod_module);

Modules/cjkcodecs/cjkcodecs.h

@@ -401,7 +401,7 @@ errorexit:
         NULL,                                                           \
         NULL                                                            \
     };                                                                  \
-    PyObject*                                                           \
+    PyMODINIT_FUNC                                                      \
     PyInit__codecs_##loc(void)                                          \
     {                                                                   \
         PyObject *m = PyModule_Create(&__module);                       \

Modules/nismodule.c

@@ -456,7 +456,7 @@ static struct PyModuleDef nismodule = {
     NULL
 };
 
-PyObject*
+PyMODINIT_FUNC
 PyInit_nis(void)
 {
     PyObject *m, *d;

Modules/pyexpat.c

@@ -1900,16 +1900,6 @@ PyDoc_STRVAR(pyexpat_module_documentation,
 #define MODULE_INITFUNC PyInit_pyexpat
 #endif
 
-#ifndef PyMODINIT_FUNC
-#   ifdef MS_WINDOWS
-#       define PyMODINIT_FUNC __declspec(dllexport) void
-#   else
-#       define PyMODINIT_FUNC void
-#   endif
-#endif
-
-PyMODINIT_FUNC MODULE_INITFUNC(void);  /* avoid compiler warnings */
-
 static struct PyModuleDef pyexpatmodule = {
         PyModuleDef_HEAD_INIT,
         MODULE_NAME,