By Guy Faulconbridge LONDON (Reuters) -The Kremlin said on Monday that U.S. President Joe Biden’s remark that Vladimir Putin “cannot remain in power” was a cause for alarm, a guarded response to the first public call from the United States for an end to Putin’s 22-year rule. “For God’s sake, this man cannot remain in power,” Biden said on Saturday at the end of a speech to a crowd in Warsaw. He cast Russia’s invasion of Ukraine as a battle in a much broader conflict between democracy and autocracy. The White House tried to clarify Biden’s remarks and the U.S. president said on Sunday he had no…