Fix another unused-private-field clang error.

dart/runtime/vm/intermediate_language.h

Index: dart/runtime/vm/intermediate_language.h
diff --git a/dart/runtime/vm/intermediate_language.h b/dart/runtime/vm/intermediate_language.h
index 05b0a215a6840f864b5ab372ccc2c27eb3176b56..d124490334b5e6fb830e730b710333f81b188ed8 100644
--- a/dart/runtime/vm/intermediate_language.h
+++ b/dart/runtime/vm/intermediate_language.h
@@ -1073,7 +1073,7 @@ class BlockEntryInstr : public Instruction {
 class ForwardInstructionIterator : public ValueObject {
  public:
   explicit ForwardInstructionIterator(BlockEntryInstr* block_entry)
-      : block_entry_(block_entry), current_(block_entry) {
+      : current_(block_entry) {
     Advance();
   }
 
@@ -1090,7 +1090,6 @@ class ForwardInstructionIterator : public ValueObject {
   Instruction* Current() const { return current_; }
 
  private:
-  BlockEntryInstr* block_entry_;
   Instruction* current_;
 };