Python: Port SlotsInOldStyleClass.ql

Only trivial test changes.

Author: tausbn

python/ql/src/Classes/SlotsInOldStyleClass.ql

@@ -12,9 +12,11 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
-from ClassObject c
-where not c.isNewStyle() and c.declaresAttribute("__slots__") and not c.failedInference()
+from Class c
+where
+  not DuckTyping::isNewStyle(c) and
+  DuckTyping::declaresAttribute(c, "__slots__")
 select c,
   "Using '__slots__' in an old style class just creates a class attribute called '__slots__'."

python/ql/test/2/query-tests/Classes/new-style/SlotsInOldStyleClass.expected

@@ -1 +1 @@
-| newstyle_test.py:4:1:4:16 | class OldStyle1 | Using '__slots__' in an old style class just creates a class attribute called '__slots__'. |
+| newstyle_test.py:4:1:4:16 | Class OldStyle1 | Using '__slots__' in an old style class just creates a class attribute called '__slots__'. |