Python: Remove points-to to from ControlFlowNode

Moves the existing points-to predicates to the newly added class
`ControlFlowNodeWithPointsTo` which resides in the `LegacyPointsTo`
module.

(Existing code that uses these predicates should import this module, and
references to `ControlFlowNode` should be changed to
`ControlFlowNodeWithPointsTo`.)

Also updates all existing points-to based code to do just this.

python/ql/src/Statements/ModificationOfLocals.ql

@@ -12,8 +12,11 @@
  */
 
 import python
+private import LegacyPointsTo
 
-predicate originIsLocals(ControlFlowNode n) { n.pointsTo(_, _, Value::named("locals").getACall()) }
+predicate originIsLocals(ControlFlowNodeWithPointsTo n) {
+  n.pointsTo(_, _, Value::named("locals").getACall())
+}
 
 predicate modification_of_locals(ControlFlowNode f) {
   originIsLocals(f.(SubscriptNode).getObject()) and