Get rid of HStringLength.

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index b75a43f69e059f6b1da08206edc590fd8bbcbedf..a5371f7d67334fffd712fd6ac672e1b842709a10 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -2316,12 +2316,6 @@ 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()