[turbofan] Drop V8_TURBOFAN_BACKEND and V8_TURBOFAN_TARGET defines.

test/cctest/test-api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 21160 matching lines @@
   v8::Local<v8::String> result = v8::String::Concat(str, str);
   CHECK(result.IsEmpty());
   CHECK(!try_catch.HasCaught());
 }
 
 
 TEST(TurboAsmDisablesNeuter) {
   v8::V8::Initialize();
   v8::HandleScope scope(CcTest::isolate());
   LocalContext context;
-#if V8_TURBOFAN_TARGET
   bool should_be_neuterable = !i::FLAG_turbo_asm;
-#else
-  bool should_be_neuterable = true;
-#endif
   const char* load =
       "function Module(stdlib, foreign, heap) {"
       "  'use asm';"
       "  var MEM32 = new stdlib.Int32Array(heap);"
       "  function load() { return MEM32[0]; }"
       "  return { load: load };"
       "}"
       "var buffer = new ArrayBuffer(4);"
       "Module(this, {}, buffer).load();"
       "buffer";
@@ skipping 626 matching lines @@
   CHECK(try_catch.HasTerminated());
 }
 
 
 TEST(EstimatedContextSize) {
   v8::Isolate* isolate = CcTest::isolate();
   v8::HandleScope scope(isolate);
   LocalContext env;
   CHECK(50000 < env->EstimatedSize());
 }