LONDON — Cars draped in the flags of Iran’s former monarchy drove through the streets of north London on Saturday night, blaring lively music and honking their horns, shortly after reports came out that the Islamic Republic’s supreme leader, Ayatollah Ali Khamenei, was killed earlier that day in an Israeli airstrike — and even before Iranian media confirmed the death of the man who had brutally ruled the country for 36 years. Alongside them, pedestrians sang and cheered. They did not just bear the Iranian colors — but those of Israel and the United States, as well. Khamenei had presided...