Avoid wasteful JSON parsing+deserialisation in finfo

[valbucci]

FuncInfo extraction jobs would parse the output of aflj with JSON to then serialise it again within the write_to_json function.

This PR takes the String output of aflj in extract_function_info and stores it as-is.

In the future is may be worth looking into setup_function_list and check if we can avoid running the same command twice when finfo and other extract modes like bytes and func-cfg are invoked together.