fix: Delete the hyperlink of the "dns"

Signed-off-by: yansira <yansira@hotmail.com>
Change-Id: Ia7d213d339130a8b52c27c113fc418688647af52

zh-cn/device-dev/kernel/Readme-CN.md

@@ -154,7 +154,6 @@
         - [网络命令](kernel-small-debug-shell-net.md)
           - [arp](kernel-small-debug-shell-net-arp.md)
           - [dhclient](kernel-small-debug-shell-net-dhclient.md)
-          - [dns](kernel-small-debug-shell-net-dns.md)
           - [ifconfig](kernel-small-debug-shell-net-ifconfig.md)
           - [ipdebug](kernel-small-debug-shell-net-ipdebug.md)
           - [netstat](kernel-small-debug-shell-net-netstat.md)