I'd argue it's still a useful sense, no matter how desperately we try to rationalize it away.
While certainly the danger from someone you know isn't zero, strangers are many, many times more dangerous in many contexts.
Just because we've industrialized the proximity of strangers with our cities, doesn't change the simple fact that strangers are more risky than people you know. And while skin-color doesn't equate to "someone I know", even a 5% benefit is likely evolutionarily impactful.
What's curious is that these studies also tend to show that in the US adult black-skinned individuals LIKEWISE act preferentially to white-skinned individuals*, suggesting that it's not just identificatory friend-or-foe at work, but likely learned behavior from experience.
*I'd be interested in seeing comparisons of the results from adults vs pre-socialized children, but I've never seen them presented in a controlled enough fashion to say they're comparable.