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

diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index 5636140..8ff0669 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -5,7 +5,7 @@
 #include "Python.h"
 #include "pycore_pylifecycle.h"
 #include "pycore_interp.h"       // _PyInterpreterState.num_threads
-#include "pycore_pystate.h"
+#include "pycore_pystate.h"      // _PyThreadState_Init()
 #include "pythread.h"
 #include <stddef.h>              // offsetof()