WASHINGTON — In a setback to abortion rights advocates, the U.S. Supreme Court on Tuesday paved the way for Republican-backed restrictions on medication-induced abortions to take effect in Arkansas that could lead to the shuttering of two of the state’s three abortion clinics.The nine justices, with no noted dissents, declined to hear an appeal by abortion provider Planned Parenthood of a lower-court ruling that had revived the state law, which sets regulations regarding the RU-486 “abortion pill,” after it was earlier struck down by a federal judge.