Some horses need no introduction, and Lafitte de Muze is one of them. With Amanda Steege riding, Cheryl Olsten’s “Lafitte” has earned hunter celebrity status thanks to his many derby wins, distinctive jumping style and philanthropic legacy. (Olsten has donated much of his prize money to the EQUUS Foundation, and Steege said that tally has now gone over $500,000.) But he’s not resting on his laurels.