Borussia Dortmund want to use the remaining two games in the Bundesliga as preparation for the Champions League final and have not forgotten how Mainz cost them the title last season. Dortmund visit Mainz on Saturday knowing they will finish at least fifth and so qualify for next term’s Champions League irrespective of whether they beat Real Madrid at Wembley on June 1. Mainz meanwhile are in the relegation play-off spot and are desperate to escape. But last season their 2-2 draw with Dortmund meant Bayern Munich won the Bundesliga instead of the Black and Yellows. “We want to achieve somethin…