By Sachin Ravikumar (Reuters) -Board members at Russian companies, including the British chairmen of gold and silver producer Polymetal and metals and hydropower group EN+, have quit in response to the conflict in Ukraine. Polymetal said on Monday Chairman Ian Cockerill and five other non-executive independent directors — Ollie Oliveira, Tracey Kerr, Italia Boninelli, Victor Flores and Andrea Abt — had left the London-listed company’s board. Polymetal gave no further details of the departures that coincide with concerns over the impact of Russia’s invasion of Ukraine and subsequent Western san…