scripted-diff: Remove setup_clean_chain if default is not changed

-BEGIN VERIFY SCRIPT-
git grep -l "self.setup_clean_chain = False" test/functional/*.py | xargs sed -i "/self.setup_clean_chain = False/d";
-END VERIFY SCRIPT-

test/functional/feature_asmap.py

@@ -36,7 +36,6 @@ def expected_messages(filename):
 
 class AsmapTest(BitcoinTestFramework):
     def set_test_params(self):
-        self.setup_clean_chain = False
         self.num_nodes = 1
 
     def test_without_asmap_arg(self):