By Evan Bleier Prior to invading Russian forces closing in on the Ukrainian capital Friday as part of an attempt to replace Ukrainian President Volodymyr Zelenskyy with a Kremlin-friendly regime, Kyiv’s mayor said he was prepared to fight back by taking up arms to defend his city. And it just so happens that the mayor, former heavyweight champion Vitali Klitschko, knows about fighting back. Along with his brother, former heavyweight champion Wladimir (who enlisted in Ukraine’s reserve army in Kyiv earlier this month), Vitali will be doing what he can to protect Kyiv’s citizens in what he said …