Return Object* instead of MaybeObject* from runtime calls.

src/runtime.h

Index: src/runtime.h
diff --git a/src/runtime.h b/src/runtime.h
index 5b92b12c5ec19b9614f6b32b9fdf98d4f5ebef5c..93c51c951502794eb1d7829722a2daf50f1339b9 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -890,10 +890,6 @@ class Runtime : public AllStatic {
       ElementsKind* fixed_elements_kind,
       size_t *element_size);
 
-  // Helper functions used stubs.
-  static void PerformGC(Object* result, Isolate* isolate);
-  static void OutOfMemory();
-
   // Used in runtime.cc and hydrogen's VisitArrayLiteral.
   MUST_USE_RESULT static MaybeHandle<Object> CreateArrayLiteralBoilerplate(
       Isolate* isolate,