By Christoph Steitz and Tom Käckenhoff FRANKFURT (Reuters) -Shares in German utility Uniper gave up earlier gains to close flat after the group signalled an exit from Russia and wrote down its exposure to the Nord Stream 2 pipeline, key areas of investor concern since Moscow’s invasion of Ukraine. Shares in Uniper had soared as much as 9.1% earlier on the news, while Finnish parent Fortum, which holds 78% in Uniper, had gained as much as 6.9%. Shares in both firms closed virtually flat. “We have to put our business on a new footing,” Harald Seegatz, deputy chairman of Uniper’s supervisory boar…