Remove the first_right_arg hack for HMod.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index a6644af5ef78a605a9beb003dfd93228339dba32..69ef805afe0fa35c7c4b6fe53115e5efe166695d 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1483,10 +1483,6 @@ 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(UseRegisterAtStart(left),
-                                     UseRegisterAtStart(right));
-      return AssignEnvironment(DefineAsRegister(mod));
     } else if (CpuFeatures::IsSupported(SUDIV)) {
       LModI* mod = new(zone()) LModI(UseRegister(left),
                                      UseRegister(right));