(Reuters) - Falls for mining stocks and a 4% drop in Asia-exposed luxury brand Burberry led London's FTSE 100 lower on Friday, as doubts about a U.S.-China trade deal halted a five-day winning streak for European markets.The main index was down 0.6%, while the FTSE 250 , which hit a three-week high on Thursday after two Bank of England policymakers unexpectedly voted for lower interest rates, shed 0.5%. Positive trade signals this week, including a report that an agreement between China and..