bpo-40268: Remove a few pycore_pystate.h includes (GH-19510)

diff --git a/Objects/classobject.c b/Objects/classobject.c
index 999b91c..ce4bf7b 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -4,7 +4,7 @@
 #include "pycore_object.h"
 #include "pycore_pyerrors.h"
 #include "pycore_pymem.h"
-#include "pycore_pystate.h"
+#include "pycore_pystate.h"   // _PyThreadState_GET()
 #include "structmember.h"
 
 #define TP_DESCR_GET(t) ((t)->tp_descr_get)