C++: Remove local flow from additional taint step

This case was not supposed to be there -- that was the whole point of
having the `localAdditionalTaintStep` predicate.

Author: jbj

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/TaintTrackingUtil.qll

@@ -17,9 +17,6 @@ predicate localTaintStep(DataFlow::Node nodeFrom, DataFlow::Node nodeTo) {
  * different objects.
  */
 predicate localAdditionalTaintStep(DataFlow::Node nodeFrom, DataFlow::Node nodeTo) {
-  // Taint can flow into using ordinary data flow.
-  DataFlow::localFlowStep(nodeFrom, nodeTo)
-  or
   localInstructionTaintStep(nodeFrom.asInstruction(), nodeTo.asInstruction())
 }