Python: Port UselessClass.ql

No test changes.

python/ql/src/Classes/UselessClass.ql

@@ -13,7 +13,7 @@
  */
 
 import python
-private import LegacyPointsTo
+private import semmle.python.dataflow.new.internal.DataFlowDispatch
 
 predicate fewer_than_two_public_methods(Class cls, int methods) {
   (methods = 0 or methods = 1) and
@@ -25,13 +25,8 @@ predicate does_not_define_special_method(Class cls) {
 }
 
 predicate no_inheritance(Class c) {
-  not exists(ClassValue cls, ClassValue other |
-    cls.getScope() = c and
-    other != ClassValue::object()
-  |
-    other.getABaseType() = cls or
-    cls.getABaseType() = other
-  ) and
+  not exists(getADirectSubclass(c)) and
+  not exists(getADirectSuperclass(c)) and
   not exists(Expr base | base = c.getABase() |
     not base instanceof Name or base.(Name).getId() != "object"
   )