C++: Remove yet another DefinitionExt reference.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -364,7 +364,7 @@ class Node extends TIRDataFlowNode {
    * pointed to by `p`.
    */
   Expr asDefinition(boolean uncertain) {
-    exists(StoreInstruction store, Ssa::DefinitionExt def |
+    exists(StoreInstruction store, Ssa::Definition def |
       store = this.asInstruction() and
       result = asDefinitionImpl(store) and
       Ssa::defToNode(this, def, _, _, _, _) and