AP audience (visibility) パースの修正 (#5783)

* Refactor audience

* audienceのないAP Object 対応

* fix

* Update src/remote/activitypub/audience.ts

Co-Authored-By: Acid Chicken (硫酸鶏) <root@acid-chicken.com>

* Update src/remote/activitypub/audience.ts

Co-Authored-By: Acid Chicken (硫酸鶏) <root@acid-chicken.com>

Co-authored-by: Acid Chicken (硫酸鶏) <root@acid-chicken.com>
Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>