[crankshaft] Remove the useless HCallStub instruction.

src/crankshaft/mips/lithium-mips.cc

Index: src/crankshaft/mips/lithium-mips.cc
diff --git a/src/crankshaft/mips/lithium-mips.cc b/src/crankshaft/mips/lithium-mips.cc
index 027021177daa7ab4080926607157fc578eb37045..ef9da821d6a119c9ca27b38ded0b35e87d0cf147 100644
--- a/src/crankshaft/mips/lithium-mips.cc
+++ b/src/crankshaft/mips/lithium-mips.cc
@@ -2408,12 +2408,6 @@ LInstruction* LChunkBuilder::DoUnknownOSRValue(HUnknownOSRValue* instr) {
 }
 
 
-LInstruction* LChunkBuilder::DoCallStub(HCallStub* instr) {
-  LOperand* context = UseFixed(instr->context(), cp);
-  return MarkAsCall(DefineFixed(new(zone()) LCallStub(context), v0), instr);
-}
-
-
 LInstruction* LChunkBuilder::DoArgumentsObject(HArgumentsObject* instr) {
   // There are no real uses of the arguments object.
   // arguments.length and element access are supported directly on