Remove --harmony-modules flag and let embedder decide when modules are used

src/api.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 1835 matching lines @@
     Source* source,
     CompileOptions options) {
   auto context = v8_isolate->GetCurrentContext();
   RETURN_TO_LOCAL_UNCHECKED(Compile(context, source, options), Script);
 }
 
 
 MaybeLocal<Script> ScriptCompiler::CompileModule(Local<Context> context,
                                                  Source* source,
                                                  CompileOptions options) {
-  CHECK(i::FLAG_harmony_modules);
   auto isolate = context->GetIsolate();
   TRACE_EVENT_SCOPED_CONTEXT("V8", "Isolate", isolate);
   auto maybe = CompileUnboundInternal(isolate, source, options, true);
   Local<UnboundScript> generic;
   if (!maybe.ToLocal(&generic)) return MaybeLocal<Script>();
   v8::Context::Scope scope(context);
   return generic->BindToCurrentContext();
 }
 
 
@@ skipping 6827 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8