BERLIN, Jan 30 (Reuters) - Once he was Germany's top Nazi hunter. Now the conservative opposition want to kick former domestic security chief Hans-Georg Maassen out of their party for allegedly repeating anti-Semitic and racist tropes. Until 2018, Maassen headed the Federal Office for the Protection of the Constitution, chasing down extremist threats to Germany's constitutional order, whether from foreign spies, religious fundamentalists, the far right or the far left. But the long-time member and one-time parliamentary candidate of former Chancellor Angela Merkel's Christian Democrats (CDU) lost that job after being accused of ignoring video evidence of far-right gangs chasing...