## Summary
Maintain consistency while deserializing Jupyter notebook to JSON. The
following changes were made:
1. Use string array to store the source value as that's the default
(5781720423/nbformat/v4/nbjson.py (L56-L57))
2. Remove unused structs and enums
3. Reorder the keys in alphabetical order as that's the default.
(5781720423/nbformat/v4/nbjson.py (L51))
### Side effect
Removing the `preserve_order` feature means that the order of keys in
JSON output (`--format json`) will be in alphabetical order. This is
because the value is represented using `serde_json::Value` which
internally is a `BTreeMap`, thus sorting it as per the string key. For
posterity if this turns out to be not ideal, then we could define a
struct representing the JSON object and the order of struct fields will
determine the order in the JSON string.
## Test Plan
Add a test case to assert the raw JSON string.
48f4f2d63d