In the first sentence, the word "usual" serves primarily to...

Scout is referring to the "usual type" of Southern tall tales they hear in Maycomb. There went with the house the usual legend about the yankees: one Finch female, recently engaged, donned her complete trousseau to save it from raiders in the neighborhood; she became stuck in the door to the Daughters' Staircase but was doused with water and finally pushed through.