“Down to Earth” is a ham-handed fantasy that manages the damn near impossible feat of making Chris Rock unfunny. Rock plays Lance Barton, a struggling stand-up comic who dies before his time. An angel in training (Eugene Levy, always welcome, even here) got his signals crossed. Heaven’s head angel (Chazz Palminteri) makes amends by finding Lance a new body, a freshly dead billionaire industrialist, who happens to be fat, fiftyish and white. It should be a blast to watch Rock deliver his black humor in the body of a clueless honky. But writer-directors Chris and Paul Weitz (“American Pie”) blow the joke in this updated spin on Warren Beatty’s 1978 hit “Heaven Can Wait,” which was itself a remake of 1941’s “Here Comes Mr. Jordan.” And try as he might, Rock can’t generate romantic sparks with Regina King, who plays the sister Lance loves in whatever body he happens to inhabit. The call on this one is: dead on arrival.