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_includeconf.py

@@ -20,7 +20,6 @@ from test_framework.test_framework import BitcoinTestFramework
 
 class IncludeConfTest(BitcoinTestFramework):
     def set_test_params(self):
-        self.setup_clean_chain = False
         self.num_nodes = 1
 
     def setup_chain(self):