C#: Reduce reliance on CFG nodes in DataFlow::Node.

Author: aschackmull

csharp/ql/consistency-queries/DataFlowConsistency.ql

@@ -70,16 +70,6 @@ private module Input implements InputSig<Location, CsharpDataFlow> {
           init.getInitializer().getNumberOfChildren() > 1
         )
       or
-      exists(ControlFlow::Nodes::ElementNode cfn, ControlFlow::Nodes::Split split |
-        exists(arg.asExprAtNode(cfn))
-      |
-        split = cfn.getASplit() and
-        not split = call.getControlFlowNode().getASplit()
-        or
-        split = call.getControlFlowNode().getASplit() and
-        not split = cfn.getASplit()
-      )
-      or
       call.(NonDelegateDataFlowCall).getDispatchCall().isReflection()
     )
   }

csharp/ql/lib/semmle/code/csharp/controlflow/Guards.qll

@@ -784,11 +784,7 @@ class GuardedDataFlowNode extends DataFlow::ExprNode {
   private AccessOrCallExpr sub0;
   private GuardValue v0;
 
-  GuardedDataFlowNode() {
-    exists(ControlFlow::Nodes::ElementNode cfn | exists(this.getExprAtNode(cfn)) |
-      g.controlsNode(cfn, sub0, v0)
-    )
-  }
+  GuardedDataFlowNode() { g.controlsNode(this.getExpr().getControlFlowNode(), sub0, v0) }
 
   /**
    * Gets an expression that guards this data flow node. That is, this data flow