LONDON (Reuters) - European stocks slid from record highs and sterling dropped amid reports that Britain's prime minister was ready to play rough in Brexit talks.U.S.-China trade optimism and reassuring economic data from China had driven Asia and the main emerging market stocks index to 18-month highs overnight, but the greens immediately turned red when London, Frankfurt and Paris opened. The FTSE 100 , which had seen its best day in nearly a year on Monday, dropped 0.2% and the UK's..