Clean up dead code after spread desugaring

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 6c9e195075097621f9245b539467db39f736eba4..77f2a44681029ce9b979b03765c9de12e24f2e5f 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -96,11 +96,6 @@ enum BindingFlags {
   V(SPREAD_ITERABLE_INDEX, JSFunction, spread_iterable)
 
 
-#define NATIVE_CONTEXT_JS_BUILTINS(V)                   \
-  V(CONCAT_ITERABLE_TO_ARRAY_BUILTIN_INDEX, JSFunction, \
-    concat_iterable_to_array_builtin)
-
-
 #define NATIVE_CONTEXT_IMPORTED_FIELDS(V)                                     \
   V(ARRAY_CONCAT_INDEX, JSFunction, array_concat)                             \
   V(ARRAY_POP_INDEX, JSFunction, array_pop)                                   \
@@ -154,8 +149,7 @@ enum BindingFlags {
   V(STACK_OVERFLOW_BOILERPLATE_INDEX, JSObject, stack_overflow_boilerplate)   \
   V(SYNTAX_ERROR_FUNCTION_INDEX, JSFunction, syntax_error_function)           \
   V(TYPE_ERROR_FUNCTION_INDEX, JSFunction, type_error_function)               \
-  V(URI_ERROR_FUNCTION_INDEX, JSFunction, uri_error_function)                 \
-  NATIVE_CONTEXT_JS_BUILTINS(V)
+  V(URI_ERROR_FUNCTION_INDEX, JSFunction, uri_error_function)
 
 #define NATIVE_CONTEXT_FIELDS(V)                                               \
   V(GLOBAL_PROXY_INDEX, JSObject, global_proxy_object)                         \
@@ -502,9 +496,6 @@ class Context: public FixedArray {
   static int ImportedFieldIndexForName(Handle<String> name);
   static int IntrinsicIndexForName(Handle<String> name);
 
-  static bool IsJSBuiltin(Handle<Context> native_context,
-                          Handle<JSFunction> function);
-
 #define NATIVE_CONTEXT_FIELD_ACCESSORS(index, type, name) \
   inline void set_##name(type* value);                    \
   inline bool is_##name(type* value);                     \