NEW YORK — Wal-Mart Stores Inc. said it will cut prices on some of its most popular toys and speed up the opening of Christmas shops in its stores as it tries to jump-start its biggest selling season. Ten toys, from Barbie Mariposa to Fur Real Newborn Animals, are priced at $10 apiece, the Bentonville, Ark.-based company said. The stakes are high: The holiday season is when many retailers make their profit for the year, and the National Retail Federation said they should brace for their worst holiday season since 2002.