Breaking change: fix closed enum validation under editions

See https://protobuf.dev/news/2024-10-02/#python-setter-validation

PiperOrigin-RevId: 707612946

python/convert.c

@@ -180,12 +180,7 @@ static bool PyUpb_PyToUpbEnum(PyObject* obj, const upb_EnumDef* e,
   } else {
     int32_t i32;
     if (!PyUpb_GetInt32(obj, &i32)) return false;
-#ifdef UPB_FUTURE_PYTHON_CLOSED_ENUM_ENFORCEMENT
     if (upb_EnumDef_IsClosed(e) && !upb_EnumDef_CheckNumber(e, i32)) {
-#else
-    if (upb_FileDef_Syntax(upb_EnumDef_File(e)) == kUpb_Syntax_Proto2 &&
-        !upb_EnumDef_CheckNumber(e, i32)) {
-#endif
       PyErr_Format(PyExc_ValueError, "invalid enumerator %d", (int)i32);
       return false;
     }

upb/port/def.inc

@@ -462,8 +462,4 @@ void __asan_unpoison_memory_region(void const volatile *addr, size_t size);
 // user code can be updated before upgrading versions of protobuf.
 #ifdef UPB_FUTURE_BREAKING_CHANGES
 
-// Properly enforce closed enums in python.
-// Owner: mkruskal@
-#define UPB_FUTURE_PYTHON_CLOSED_ENUM_ENFORCEMENT 1
-
 #endif

upb/port/undef.inc

@@ -64,4 +64,3 @@
 #undef UPB_LINKARR_START
 #undef UPB_LINKARR_STOP
 #undef UPB_FUTURE_BREAKING_CHANGES
-#undef UPB_FUTURE_PYTHON_CLOSED_ENUM_ENFORCEMENT