Remove unused class member (NFC)

Fix include/mlir/Reducer/ReductionNode.h:79:18: warning: private field 'parent' is not used [-Wunused-private-field]

mlir/include/mlir/Reducer/ReductionNode.h

@@ -74,10 +74,6 @@ private:
   // This indicates if the module has been evalueated (measured and tested).
   bool evaluated;
 
-  // This points to the ReductionNode that was used as a starting point to
-  // create this variant. It is null if the reduction node is the root.
-  ReductionNode *parent;
-
   // This points to the child variants that were created using this node as a
   // starting point.
   std::vector<std::unique_ptr<ReductionNode>> variants;

mlir/tools/mlir-reduce/ReductionNode.cpp

@@ -20,7 +20,7 @@ using namespace mlir;
 
 /// Sets up the metadata and links the node to its parent.
 ReductionNode::ReductionNode(ModuleOp module, ReductionNode *parent)
-    : module(module), evaluated(false), parent(parent) {
+    : module(module), evaluated(false) {
 
   if (parent != nullptr)
     parent->linkVariant(this);