Since the mall owner owner does not have a crystal ball to see into the future, I seriously doubt that political censorship ever entered his mind when he got a standard boiler-plate rental agreement drawn up.
Such a clause in a rental agreement would be a lighting rod for civil rights lawsuits.........
"As the Mall is patronized mostly by white, conservative patrons, the Mall owner reserves the right to evict any store owner that sells merchandise or books such as, for example, Malcolm X books and T-shirts, that white patrons find offensive".
Such a clause would never fly.
Unless, of course, you claim that it would fly if you change "conservative" to "liberal", change "white" to "black" and change "Malcolm X" to "Confederate".
Man, you're just the guy I need to answer a question: I need to repair my roof, is it going to be sunny tomorrow?