ngx-auth-firebaseui does not appear to be maintained

This is an issue with the documentation.

The docs refer to `ngx-auth-firebaseui`.

I believe this reference should be deleted as

- the library is not compatible with the current version of @angular/fire
- it appears the library is no longer being maintained

在文件中搜尋 `ngx-auth-firebaseui`，並核實 issue 中描述的參照。完成的標準是移除過時的參照，且文件不再將該函式庫描述為受支援的函式庫。

由索引模型根據 Issue 內容生成。