[material-ui][Hidden] Remove component

[aarongarciah]

The Hidden component was once removed and brought back in v5. Since it was already deprecated in v5, it's safe to remove it for v6.

[mui-bot]

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https://deploy-preview-42305--material-ui.netlify.app/

Hidden: parsed: -100.00% :heart_eyes:, gzip: -100.00% :heart_eyes: @material-ui/core: parsed: -0.50% :heart_eyes:, gzip: -0.67% :heart_eyes:

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