Remove anemoi/inference/post_processors/earthkit_state.py

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In https://github.com/ecmwf/anemoi-inference/blob/main/src/anemoi/inference/post_processors/earthkit_state.py we have a custom class.

Instead we should use the ArrayField from ekd,
https://earthkit-data.readthedocs.io/en/latest/_api/data/sources/array_list/index.html#classes
and have a wrap and unwrap function.