NEW YORK — Walmart’s sweeping rollback of its diversity policies is the strongest indication yet of a profound shift taking hold at U.S. companies that are re-evaluating the legal and political risks associated with bold programs to bolster historically underrepresented groups. The changes announced by the world’s biggest retailer on Monday followed a string of legal victories by conservative groups that have filed an onslaught of lawsuits challenging corporate and federal programs aimed at elevating minority and women-owned businesses and employees. The retreat from such programs crystalized with the election of former President Donald Trump, whose administration is certain to make dismantling diversity, equity and inclusion programs a priority.