C#: Remove references to getAFirstReadAtNode.

Author: aschackmull

csharp/ql/lib/semmle/code/csharp/Assignable.qll

@@ -488,15 +488,10 @@ class AssignableDefinition extends TAssignableDefinition {
    */
   pragma[nomagic]
   AssignableRead getAFirstRead() {
-    exists(ControlFlowNode cfn | cfn = result.getControlFlowNode() |
-      exists(Ssa::ExplicitDefinition def | result = def.getAFirstReadAtNode(cfn) |
-        this = def.getADefinition()
-      )
-      or
-      exists(Ssa::ImplicitParameterDefinition def | result = def.getAFirstReadAtNode(cfn) |
-        this.(AssignableDefinitions::ImplicitParameterDefinition).getParameter() =
-          def.getParameter()
-      )
+    exists(Ssa::ExplicitDefinition def | result = def.getAFirstRead() | this = def.getADefinition())
+    or
+    exists(Ssa::ImplicitParameterDefinition def | result = def.getAFirstRead() |
+      this.(AssignableDefinitions::ImplicitParameterDefinition).getParameter() = def.getParameter()
     )
   }
 

csharp/ql/lib/semmle/code/csharp/dataflow/Nullness.qll

@@ -255,7 +255,7 @@ private Ssa::Definition getAnUltimateDefinition(Ssa::Definition def) {
  * exception.
  */
 private predicate defReaches(Ssa::Definition def, ControlFlowNode cfn) {
-  exists(def.getAFirstReadAtNode(cfn))
+  def.getAFirstRead().getControlFlowNode() = cfn
   or
   exists(ControlFlowNode mid | defReaches(def, mid) |
     SsaImpl::adjacentReadPairSameVar(_, mid, cfn) and