[V1][Metrics] Updated list of deprecated metrics in v0.8

[markmc]

These are already marked as deprecated in the code, but they should be listed here too.

See the current state at https://docs.vllm.ai/en/latest/serving/metrics.html

        # Deprecated in 0.8 - KV cache offloading is not used in V1
        # TODO: in 0.9, only enable if show_hidden_metrics=True
        self.gauge_scheduler_swapped = self._gauge_cls(
            name="vllm:num_requests_swapped",
...

The following metrics are deprecated and due to be removed in a future version:

• (No metrics are currently deprecated)

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