fix(logout): reduce unwanted API call during logout

- stop trying to refresh session
- display "successfully signed out" rather "your session is expired"

frontend/static/locales/zh-TW.json

@@ -564,7 +564,8 @@
     "magic_hint": "沒有密碼？輸入您的電子郵件，我們將向您發送一次性登入連結。",
     "magic_unavailable": "此伺服器不支援電子郵件登入。",
     "passwords_match": "Passwords match",
-    "sign_in": "登入"
+    "sign_in": "登入",
+    "logged_out": "已成功登出。"
   },
   "storage": {
     "title": "儲存空間",
@@ -1341,4 +1342,4 @@
     "wrong_drop_zone_msg": "上傳僅在「檔案」中有效 — 請開啟檔案區並在該處拖放。",
     "wrong_drop_zone_action": "前往檔案"
   }
-}
+}