Make SerializedData into a POD struct.

PiperOrigin-RevId: 676124916
diff --git a/rust/cpp_kernel/serialized_data.h b/rust/cpp_kernel/serialized_data.h
index 48f310f..60d6ab7 100644
--- a/rust/cpp_kernel/serialized_data.h
+++ b/rust/cpp_kernel/serialized_data.h
@@ -34,8 +34,6 @@
   // Owns the memory, must be freed by Rust.
   const uint8_t* data;
   size_t len;
-
-  SerializedData(const uint8_t* data, size_t len) : data(data), len(len) {}
 };
 
 inline bool SerializeMsg(const google::protobuf::MessageLite* msg, SerializedData* out) {
@@ -53,7 +51,8 @@
   if (!msg->SerializeWithCachedSizesToArray(bytes)) {
     return false;
   }
-  *out = SerializedData(bytes, len);
+  out->data = bytes;
+  out->len = len;
   return true;
 }
 
diff --git a/rust/test/cpp/interop/test_utils.cc b/rust/test/cpp/interop/test_utils.cc
index beac499..32e419b 100644
--- a/rust/test/cpp/interop/test_utils.cc
+++ b/rust/test/cpp/interop/test_utils.cc
@@ -25,7 +25,7 @@
 
 extern "C" SerializedData SerializeTestAllTypes(
     const protobuf_unittest::TestAllTypes* msg) {
-  SerializedData data(nullptr, 0);
+  SerializedData data;
   ABSL_CHECK(SerializeMsg(msg, &data));
   return data;
 }