You don't seem to be able to do that at all. Even under the premium version which has a specific opt-in for beta features doesn't remove it (I opted out to check, but it's still there).
They've made this beta site-wide for feedback and tuning. There will likely be an option for on/off in the future, but right now I suspect they are far more focused on making the recommendations more accurate over putting in an option on/off checkbox.
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