Improve implementation of HSeqStringSetChar.

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index 06cb1719233acd551fe5c7cd0af115a6f0877451..ed17be2b3de63c14c36a3710e825ce778a7b414c 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -1283,25 +1283,20 @@ class LDateField V8_FINAL : public LTemplateInstruction<1, 1, 0> {
 
 class LSeqStringSetChar V8_FINAL : public LTemplateInstruction<1, 3, 0> {
  public:
-  LSeqStringSetChar(String::Encoding encoding,
-                    LOperand* string,
+  LSeqStringSetChar(LOperand* string,
                     LOperand* index,
-                    LOperand* value) : encoding_(encoding) {
+                    LOperand* value) {
     inputs_[0] = string;
     inputs_[1] = index;
     inputs_[2] = value;
   }
 
-  String::Encoding encoding() { return encoding_; }
   LOperand* string() { return inputs_[0]; }
   LOperand* index() { return inputs_[1]; }
   LOperand* value() { return inputs_[2]; }
 
   DECLARE_CONCRETE_INSTRUCTION(SeqStringSetChar, "seq-string-set-char")
   DECLARE_HYDROGEN_ACCESSOR(SeqStringSetChar)
-
- private:
-  String::Encoding encoding_;
 };