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/Testing/Mox.qll

@@ -1,9 +1,10 @@
 import python
+private import LegacyPointsTo
 
 /** Whether `mox` or `.StubOutWithMock()` is used in thin module `m`. */
 predicate useOfMoxInModule(Module m) {
   exists(ModuleObject mox | mox.getName() = "mox" or mox.getName() = "mox3.mox" |
-    exists(ControlFlowNode use |
+    exists(ControlFlowNodeWithPointsTo use |
       use.refersTo(mox) and
       use.getScope().getEnclosingModule() = m
     )