[turbofan] Improve interplay of ControlReducer and CommonOperatorReducer.

src/compiler/control-reducer.h

Index: src/compiler/control-reducer.h
diff --git a/src/compiler/control-reducer.h b/src/compiler/control-reducer.h
index 0fce0fb536addc2227cdda6707d6becaf1dcb7dc..25b99ffd026265aba3a1aae3f79f365a40b4c63b 100644
--- a/src/compiler/control-reducer.h
+++ b/src/compiler/control-reducer.h
@@ -30,7 +30,6 @@ class ControlReducer {
                            int max_phis_for_select = 0);
 
   // Testing interface.
-  static Node* ReducePhiForTesting(JSGraph* graph, Node* node);
   static Node* ReduceIfNodeForTesting(JSGraph* graph, Node* node);
 };
 }