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

在文档中搜索 `ngx-auth-firebaseui`，并核实 issue 中描述的引用。完成的标准是移除过时的引用，并且文档不再将该库描述为受支持的库。

由索引模型根据 Issue 内容生成。