Remove the first_right_arg hack for HMod.

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index 5fcd0a2b0afcf3e1c7fc78986cf1eaeda5bf3774..d4c17ab4708a03ab49de4ff34fe5ede8f4c24c8d 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -1558,10 +1558,6 @@ LInstruction* LChunkBuilder::DoMod(HMod* instr) {
               instr->CheckFlag(HValue::kBailoutOnMinusZero))
           ? AssignEnvironment(result)
           : result;
-    } else if (instr->fixed_right_arg().has_value) {
-      LModI* mod = new(zone()) LModI(UseRegister(left),
-                                     UseRegisterAtStart(right),
-                                     NULL);
       return AssignEnvironment(DefineSameAsFirst(mod));
     } else {
       // The temporary operand is necessary to ensure that right is not