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.

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