It’s an oddly catchy sound, a persistent noise coming from boomboxes and car stereos. Almost no one in “Cut Throat City,” the latest crime/gangster flick from legendary hip hop producer/turned filmmaker RZA, comments on it, but we know they hear it and we know what it symbolizes. It’s the sound of rap music on repeat, lingering in the air like a thick, inescapable haze of gun smoke.