[3.12] gh-110549: Remove unused includes of <stddef.h> in _testcapi (GH-110552).

(cherry picked from commit 89df5b7)

Co-authored-by: Nikita Sobolev <[email protected]>

Author: sobolevn

Include/cpython/pystate.h

@@ -256,7 +256,7 @@ struct _ts {
 #    define C_RECURSION_LIMIT 500
 #  else
     // This value is duplicated in Lib/test/support/__init__.py
-#    define C_RECURSION_LIMIT 1500
+#    define C_RECURSION_LIMIT 1500000
 #  endif
 #endif
 

Modules/_testcapi/abstract.c

@@ -1,5 +1,3 @@
-#include <stddef.h>               // ptrdiff_t
-
 #define PY_SSIZE_T_CLEAN
 #include "parts.h"
 #include "util.h"

Modules/_testcapi/dict.c

@@ -1,5 +1,3 @@
-#include <stddef.h>               // ptrdiff_t
-
 #define PY_SSIZE_T_CLEAN
 #include "parts.h"
 #include "util.h"

Modules/_testcapi/set.c

@@ -1,5 +1,4 @@
-#include <stddef.h>               // ptrdiff_t
-
+#define PY_SSIZE_T_CLEAN
 #include "parts.h"
 #include "util.h"