LONDON — In a major blow to British Prime Minister Boris Johnson, U.K. lawmakers voted Saturday to postpone a decision on whether to back his Brexit deal with the European Union, throwing a wrench into government plans to leave the bloc at the end of this month. At a special session of Parliament intended to ratify the deal, lawmakers voted 322-306 to withhold their approval on the Brexit deal until legislation to implement it has been passed. The vote aims to ensure that the U.K.