[crankshaft] Remove the useless HCallStub instruction.

src/crankshaft/arm64/lithium-arm64.cc

Index: src/crankshaft/arm64/lithium-arm64.cc
diff --git a/src/crankshaft/arm64/lithium-arm64.cc b/src/crankshaft/arm64/lithium-arm64.cc
index 298e6b519f1256461c40fdb08758a71b9f932dd4..898b0d6c67d9358f6bd04dd55ee1e93fbe66a67a 100644
--- a/src/crankshaft/arm64/lithium-arm64.cc
+++ b/src/crankshaft/arm64/lithium-arm64.cc
@@ -1084,12 +1084,6 @@ LInstruction* LChunkBuilder::DoCallRuntime(HCallRuntime* instr) {
 }
 
 
-LInstruction* LChunkBuilder::DoCallStub(HCallStub* instr) {
-  LOperand* context = UseFixed(instr->context(), cp);
-  return MarkAsCall(DefineFixed(new(zone()) LCallStub(context), x0), instr);
-}
-
-
 LInstruction* LChunkBuilder::DoCapturedObject(HCapturedObject* instr) {
   instr->ReplayEnvironment(current_block_->last_environment());