[BUG] Fix empty key in serialized Horizontal Stratigraphic Model

Removed an invalid empty key from the serialization output to ensure proper data structure and avoid potential parsing issues.

Author: Leguark

test/test_modules/test_serialize_model.test_generate_horizontal_stratigraphic_model.verify/Horizontal Stratigraphic Model serialization.approved.txt

@@ -61,7 +61,6 @@
         ],
         "is_dirty": true,
         "basement_color": "#ffbe00",
-        "": 0,
         "binary_meta_data": {
             "sp_binary_length": 432,
             "ori_binary_length": 120