BARCELONA, Spain (Reuters) - Daniel Chambers, head of trading at Sequoia Capital Fund Management, has stopped trading the pound in his nearly $200 million (£160 million) systematic currency portfolio over the course of the year because of the Brexit headline risk.The pound has had a roller-coaster ride this year as the course of Brexit negotiations has been the single biggest factor for trading the currency, causing many large investors - as well as Bank of England Governor Mark Carney - to..