Remove Debian 9

- Remove Debian 9, which is EOL after June 30, 2022.
- Cleanup

README-zh.md

@@ -71,8 +71,8 @@ https://gitlab.com/hwdsl2/setup-ipsec-vpn/-/raw/master/vpnsetup.sh
 一个云服务器，虚拟专用服务器 (VPS) 或者专用服务器，全新安装以下操作系统之一：
 
 - Ubuntu 22.04, 20.04 或者 18.04
-- Debian 11[\*](#debian-10-note), 10[\*](#debian-10-note) 或者 9
-- CentOS 7 或者 CentOS Stream 8[\*\*](#centos-8-note)
+- Debian 11 或者 10
+- CentOS 7 或者 CentOS Stream 8
 - Rocky Linux 或者 AlmaLinux 8
 - Oracle Linux 8 或者 7
 - Red Hat Enterprise Linux (RHEL) 8 或者 7
@@ -87,11 +87,6 @@ https://gitlab.com/hwdsl2/setup-ipsec-vpn/-/raw/master/vpnsetup.sh
 
 另外，你也可以使用预构建的 [Docker 镜像](https://github.com/hwdsl2/docker-ipsec-vpn-server/blob/master/README-zh.md)。高级用户可以在 [Raspberry Pi](https://www.raspberrypi.org) 上安装。[[1]](https://elasticbyte.net/posts/setting-up-a-native-cisco-ipsec-vpn-server-using-a-raspberry-pi/) [[2]](https://www.stewright.me/2018/07/create-a-raspberry-pi-vpn-server-using-l2tpipsec/)
 
-<a name="debian-10-note"></a>
-\* Debian 11/10 用户需要 [使用标准的 Linux 内核](docs/clients-zh.md#debian-10-内核)。 
-<a name="centos-8-note"></a>
-\*\* 对 CentOS Linux 8 的支持 [已经结束](https://www.centos.org/centos-linux-eol/)。
-
 :warning: **不要** 在你的 PC 或者 Mac 上运行这些脚本！它们只能用在服务器上！
 
 ## 安装说明

README.md

@@ -71,8 +71,8 @@ A pre-built [Docker image](https://github.com/hwdsl2/docker-ipsec-vpn-server) is
 A cloud server, virtual private server (VPS) or dedicated server, freshly installed with:
 
 - Ubuntu 22.04, 20.04 or 18.04
-- Debian 11[\*](#debian-10-note), 10[\*](#debian-10-note) or 9
-- CentOS 7 or CentOS Stream 8[\*\*](#centos-8-note)
+- Debian 11 or 10
+- CentOS 7 or CentOS Stream 8
 - Rocky Linux or AlmaLinux 8
 - Oracle Linux 8 or 7
 - Red Hat Enterprise Linux (RHEL) 8 or 7
@@ -87,11 +87,6 @@ This also includes Linux VMs in public clouds, such as [DigitalOcean](https://bl
 
 A pre-built [Docker image](https://github.com/hwdsl2/docker-ipsec-vpn-server) is also available. Advanced users can install on a [Raspberry Pi](https://www.raspberrypi.org). [[1]](https://elasticbyte.net/posts/setting-up-a-native-cisco-ipsec-vpn-server-using-a-raspberry-pi/) [[2]](https://www.stewright.me/2018/07/create-a-raspberry-pi-vpn-server-using-l2tpipsec/)
 
-<a name="debian-10-note"></a>
-\* Debian 11/10 users should [use the standard Linux kernel](docs/clients.md#debian-10-kernel). 
-<a name="centos-8-note"></a>
-\*\* CentOS Linux 8 [is no longer supported](https://www.centos.org/centos-linux-eol/).
-
 :warning: **DO NOT** run these scripts on your PC or Mac! They should only be used on a server!
 
 ## Installation