Megamorphic code cleanup.

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
diff --git a/runtime/vm/flow_graph_compiler_x64.cc b/runtime/vm/flow_graph_compiler_x64.cc
index 0208bdef5d48d1c9b947a57dbb7efeb56a287e00..1218af01ad715e8751211f74ee68000af3135d7e 100644
--- a/runtime/vm/flow_graph_compiler_x64.cc
+++ b/runtime/vm/flow_graph_compiler_x64.cc
@@ -25,7 +25,7 @@ namespace dart {
 DEFINE_FLAG(bool, trap_on_deoptimization, false, "Trap on deoptimization.");
 DEFINE_FLAG(bool, unbox_mints, true, "Optimize 64-bit integer arithmetic.");
 DECLARE_FLAG(bool, enable_simd_inline);
-DECLARE_FLAG(bool, use_megamorphic_stub);
+
 
 void MegamorphicSlowPath::EmitNativeCode(FlowGraphCompiler* compiler) {
   Assembler* assembler = compiler->assembler();
@@ -1348,11 +1348,7 @@ void FlowGraphCompiler::EmitMegamorphicInstanceCall(
     __ Comment("Slow case: megamorphic call");
   }
   __ LoadObject(RBX, cache);
-  if (FLAG_use_megamorphic_stub) {
-    __ call(Address(THR, Thread::megamorphic_lookup_entry_point_offset()));
-  } else  {
-    StubCode::EmitMegamorphicLookup(assembler());
-  }
+  __ call(Address(THR, Thread::megamorphic_lookup_entry_point_offset()));
   __ call(RCX);
 
   __ Bind(&done);