UNITED NATIONS — The head of the United Nations agency that assists Palestinian refugees, UNRWA, warned Friday that the expected implementation later this month of Israeli legislation aimed at shuttering the agency would be “catastrophic” to humanitarian efforts in Gaza. “A chaotic dismantling of UNRWA will irreversibly harm the lives and future of the Palestinians,” said Commissioner-General Philippe Lazzarini. “I believe it will obliterate their trust …