Get rid of HStringLength.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 4ecb733508ebb544099c352acd67045dc2c32d7f..e40316592f4b0c00af213630d307d78d8ba547b7 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2320,12 +2320,6 @@ LInstruction* LChunkBuilder::DoStringCharFromCode(HStringCharFromCode* instr) {
 }
 
 
-LInstruction* LChunkBuilder::DoStringLength(HStringLength* instr) {
-  LOperand* string = UseRegisterAtStart(instr->value());
-  return DefineAsRegister(new(zone()) LStringLength(string));
-}
-
-
 LInstruction* LChunkBuilder::DoAllocate(HAllocate* instr) {
   info()->MarkAsDeferredCalling();
   LOperand* size = instr->size()->IsConstant()