Remove the global Strength enum class completely.

src/runtime/runtime-object.cc

Index: src/runtime/runtime-object.cc
diff --git a/src/runtime/runtime-object.cc b/src/runtime/runtime-object.cc
index 17436aaf0e2486bc6be1c71caf93c5f8ec234cb5..f36a419c745182ce55099b5f57953083f7c2604f 100644
--- a/src/runtime/runtime-object.cc
+++ b/src/runtime/runtime-object.cc
@@ -836,15 +836,6 @@ RUNTIME_FUNCTION(Runtime_IsJSReceiver) {
 }
 
 
-RUNTIME_FUNCTION(Runtime_IsStrong) {
-  SealHandleScope shs(isolate);
-  DCHECK(args.length() == 1);
-  CONVERT_ARG_CHECKED(Object, obj, 0);
-  return isolate->heap()->ToBoolean(obj->IsJSReceiver() &&
-                                    JSReceiver::cast(obj)->map()->is_strong());
-}
-
-
 RUNTIME_FUNCTION(Runtime_ClassOf) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 1);