bpo-40268: Remove unused structmember.h includes (GH-19530)
If only offsetof() is needed: include stddef.h instead.
When structmember.h is used, add a comment explaining that
PyMemberDef is used.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index da04af4..7376359 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -3,7 +3,7 @@
#include "Python.h"
#include "code.h"
#include "opcode.h"
-#include "structmember.h"
+#include "structmember.h" // PyMemberDef
#include "pycore_code.h"
#include "pycore_interp.h" // PyInterpreterState.co_extra_freefuncs
#include "pycore_pystate.h" // _PyInterpreterState_GET()