bpo-38304: Remove PyConfig.struct_size (GH-16500)

For now, we'll rely on the fact that the config structures aren't covered by the stable ABI.

We may revisit this in the future if we further explore the idea of offering a stable embedding API.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index c154d06..5174f74 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -731,7 +731,6 @@
     runtime->preinitializing = 1;
 
     PyPreConfig config;
-    config.struct_size = sizeof(PyPreConfig);
 
     status = _PyPreConfig_InitFromPreConfig(&config, src_config);
     if (_PyStatus_EXCEPTION(status)) {
@@ -795,12 +794,8 @@
     }
 
     PyPreConfig preconfig;
-    preconfig.struct_size = sizeof(PyPreConfig);
 
-    status = _PyPreConfig_InitFromConfig(&preconfig, config);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
+    _PyPreConfig_InitFromConfig(&preconfig, config);
 
     if (!config->parse_argv) {
         return Py_PreInitialize(&preconfig);
@@ -848,7 +843,6 @@
     }
 
     PyConfig config;
-    config.struct_size = sizeof(PyConfig);
 
     status = _PyConfig_InitCompatConfig(&config);
     if (_PyStatus_EXCEPTION(status)) {
@@ -1076,7 +1070,6 @@
     }
 
     PyConfig config;
-    config.struct_size = sizeof(PyConfig);
 
     status = _PyConfig_InitCompatConfig(&config);
     if (_PyStatus_EXCEPTION(status)) {