Reduce ecma_{ref, deref}_object calls while using ecma_builtin_get (#2616)

The following stucture was highly frequented in the code base:

 - Get a builtin object // This operation increases the reference count of the object
 - Use it for create a new object
 - Deref the builtin object

After a builtin has been instantiated there is always at least one reference to "keep it alive",
so increase/decrease the reference count for getting the value only is unnecessary.

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

jerry-core/ecma/operations/ecma-string-object.c

@@ -70,8 +70,6 @@ ecma_op_create_string_object (const ecma_value_t *arguments_list_p, /**< list of
                                                 sizeof (ecma_extended_object_t),
                                                 ECMA_OBJECT_TYPE_CLASS);
 
-  ecma_deref_object (prototype_obj_p);
-
   ecma_extended_object_t *ext_object_p = (ecma_extended_object_t *) object_p;
   ext_object_p->u.class_prop.class_id = LIT_MAGIC_STRING_STRING_UL;
   ext_object_p->u.class_prop.u.value = prim_value;