[turbofan] Remove usage of Unique<T> from graph.

src/compiler/ast-graph-builder.h

Index: src/compiler/ast-graph-builder.h
diff --git a/src/compiler/ast-graph-builder.h b/src/compiler/ast-graph-builder.h
index 6c8e656166c3251ea3d6978a30a6f45f6fa0899d..be594079ec56efb5071135a03fb18ab3699c073d 100644
--- a/src/compiler/ast-graph-builder.h
+++ b/src/compiler/ast-graph-builder.h
@@ -230,12 +230,6 @@ class AstGraphBuilder : public AstVisitor {
   // frame states with the undefined values.
   void ClearNonLiveSlotsInFrameStates();
 
-  // Helper to wrap a Handle<T> into a Unique<T>.
-  template <class T>
-  Unique<T> MakeUnique(Handle<T> object) {
-    return Unique<T>::CreateUninitialized(object);
-  }
-
   Node** EnsureInputBufferSize(int size);
 
   // Named and keyed loads require a VectorSlotPair for successful lowering.