The streets of pony wonderland Equestria are oddly poop-free, and almost impossibly festive. But as we’ve learned in “Trolls,” the Smurfs franchise and “The Three Amigos,” there is bound to be conflict when you build a society where there is no defense spending and 98 percent of your budget goes to party planning. “My Little Pony: The Movie” creates a rainbow-hued sparkle-encrusted equine world, then surrounds it with a predictable story and low production values.