PHILADELPHIA (AP) — Aerosmith is one of the best things to come out of Boston, and soon it will exist only in memories and playbacks — like Tom Brady, “Cheers” and Larry Bird. The quintet has given the world 50 years of classic rock and some of the most enduring songs of all time, including “Dream On,” “Walk This Way” and “Sweet Emotion.” Aerosmith began its farewell “Peace Out” tour Saturday in Philadelphia with a two-hour set spanning its voluminous catalog — giving the world one last chance to see what earned these skinny guys from New England an exalted place in the pantheon of rock's all-time greats. Singer Steven Tyler, guitarists Joe Perry and Brad Whitford, and bassist Tom Hamilton all wore black cowboy hats as they ripped into “Back In The Saddle,” the song that has opened Aerosmith shows for decades as a giant Aerosmith logo folded down from the rafters, flanked by an even bigger set of wings.