[crankshaft] Remove the useless HCallStub instruction.

src/crankshaft/mips64/lithium-codegen-mips64.cc

Index: src/crankshaft/mips64/lithium-codegen-mips64.cc
diff --git a/src/crankshaft/mips64/lithium-codegen-mips64.cc b/src/crankshaft/mips64/lithium-codegen-mips64.cc
index 9fafbe20b5d11411b534b15b22406bbb03cab1c3..020c5ef0388037b874f3fff16d833aabae2366b6 100644
--- a/src/crankshaft/mips64/lithium-codegen-mips64.cc
+++ b/src/crankshaft/mips64/lithium-codegen-mips64.cc
@@ -928,26 +928,6 @@ void LCodeGen::DoParameter(LParameter* instr) {
 }
 
 
-void LCodeGen::DoCallStub(LCallStub* instr) {
-  DCHECK(ToRegister(instr->context()).is(cp));
-  DCHECK(ToRegister(instr->result()).is(v0));
-  switch (instr->hydrogen()->major_key()) {
-    case CodeStub::RegExpExec: {
-      RegExpExecStub stub(isolate());
-      CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
-      break;
-    }
-    case CodeStub::SubString: {
-      SubStringStub stub(isolate());
-      CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
-      break;
-    }
-    default:
-      UNREACHABLE();
-  }
-}
-
-
 void LCodeGen::DoUnknownOSRValue(LUnknownOSRValue* instr) {
   GenerateOsrPrologue();
 }