[AIR] Do not deepcopy RunConfig

[amogkam]

RunConfig is not a tunable hyperparameter, so we do not need to deep copy it when merging parameters with Ray Tune's param_space.

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[Yard1]

I'm wondering why we deepcopy in merge_dicts in the first place. I think it should be just a shallow copy.

[amogkam]

@Yard1 are you saying that instead of doing the deepcopy all up front, we should just copy level by level, as we do the deep merging? If so, I agree- but I think we can leave that for a future PR. The implementation for this just used the merge_dicts utility that we currently have.