[crankshaft] Remove the useless HCallStub instruction.

src/crankshaft/arm/lithium-arm.cc

Index: src/crankshaft/arm/lithium-arm.cc
diff --git a/src/crankshaft/arm/lithium-arm.cc b/src/crankshaft/arm/lithium-arm.cc
index d4e7ec936d373e7f9df69ce19a705c894012ba9c..8d178d5ee001692ad9b4826ffc344ce9735a060b 100644
--- a/src/crankshaft/arm/lithium-arm.cc
+++ b/src/crankshaft/arm/lithium-arm.cc
@@ -2461,12 +2461,6 @@ LInstruction* LChunkBuilder::DoUnknownOSRValue(HUnknownOSRValue* instr) {
 }
 
 
-LInstruction* LChunkBuilder::DoCallStub(HCallStub* instr) {
-  LOperand* context = UseFixed(instr->context(), cp);
-  return MarkAsCall(DefineFixed(new(zone()) LCallStub(context), r0), instr);
-}
-
-
 LInstruction* LChunkBuilder::DoArgumentsObject(HArgumentsObject* instr) {
   // There are no real uses of the arguments object.
   // arguments.length and element access are supported directly on