yaml cases: some tests need to be deleted or fixed

- `%%udf` style udf, e.g. `cases/plan/udf_query.yaml`, `cases/query/group_query.yaml`, etc. We won't support anymore, so delete them.
- `cases/yaml/demo.yaml` is only loaded to init, no run, so cases are all wrong, needs fix

Look for the test cases directory, likely named 'cases'. Identify files mentioned: plan/udf_query.yaml, query/group_query.yaml, and yaml/demo.yaml. For the first set, delete the files or remove the unsupported '%%udf' style tests. For demo.yaml, examine how it's loaded and correct the test cases so they run properly. Verify changes by running the test suite.

Written by the indexing model from the issue text.