[TECH DEBT] Remove `Dashboard.as_dict` in `LakeviewAPI` calls when SDK handles these

Remove `Dashboard.as_dict` in `LakeviewAPI` calls when SDK handles these introduced in [PR](https://github.com/databrickslabs/lsql/pull/320). See [this PR](https://github.com/databricks/databricks-sdk-py/pull/824) for the expected changes in the SDK.