Walmart has announced that after eight years in business, it is closing its music download store. Citing a certified letter sent by Walmart to its distribution and licensing partners, Digital Music News reports that the store, located at mp3.walmart.com, will close on August 28. The retail giant will continue to sell physical CDs in its brick-and-mortar stores, and will continue to provide support for older, DRM-laden WMA files that were purchased…