[serializer] remove some dead code.

test/cctest/test-serialize.cc

Index: test/cctest/test-serialize.cc
diff --git a/test/cctest/test-serialize.cc b/test/cctest/test-serialize.cc
index 77e93da851e1d846caeba9ddd8d44094bc324e6b..2f29b25fab07e201e076c025acb2486c39387438 100644
--- a/test/cctest/test-serialize.cc
+++ b/test/cctest/test-serialize.cc
@@ -93,7 +93,8 @@ void WritePayload(const Vector<const byte>& payload, const char* file_name) {
 static bool WriteToFile(Isolate* isolate, const char* snapshot_file) {
   SnapshotByteSink sink;
   StartupSerializer ser(isolate, &sink);
-  ser.Serialize();
+  ser.SerializeStrongReferences();
+  ser.SerializeWeakReferencesAndDeferred();
   SnapshotData snapshot_data(ser);
   WritePayload(snapshot_data.RawData(), snapshot_file);
   return true;