In “Ambulance,” director Michael Bay’s chaotic, frenetic daytime travelogue of Los Angeles, the viewer is constantly reminded of other, better movies. There’s a shootout in the streets following a bank heist, like in “Heat.” There’s a chase through the L.A. River basin, like in “T2.” The majority of the movie takes place on board a moving vehicle as it barrels down L.A.’s freeways, like in “Speed.” Even its characters can’t stop talking about other Bay films, making conversational references to “The Rock” and “Bad Boys.” “Ambulance” best exists as an homage to the movies that came before it, b…