gh-101819: Remove unused 'locale_module' from _io state (#104246)

The locale module reference was introduced by 932ff83 in 2013,
and rendered unused by 710e826 (gh-23050) in 2020.

Author: erlend-aasland

Modules/_io/_iomodule.c

@@ -580,7 +580,6 @@ iomodule_traverse(PyObject *mod, visitproc visit, void *arg) {
     _PyIO_State *state = get_io_state(mod);
     if (!state->initialized)
         return 0;
-    Py_VISIT(state->locale_module);
     Py_VISIT(state->unsupported_operation);
 
     Py_VISIT(state->PyIncrementalNewlineDecoder_Type);
@@ -605,8 +604,6 @@ iomodule_clear(PyObject *mod) {
     _PyIO_State *state = get_io_state(mod);
     if (!state->initialized)
         return 0;
-    if (state->locale_module != NULL)
-        Py_CLEAR(state->locale_module);
     Py_CLEAR(state->unsupported_operation);
 
     Py_CLEAR(state->PyIncrementalNewlineDecoder_Type);

Modules/_io/_iomodule.h

@@ -143,8 +143,6 @@ extern PyModuleDef _PyIO_Module;
 
 typedef struct {
     int initialized;
-    PyObject *locale_module;
-
     PyObject *unsupported_operation;
 
     /* Types */