remove Tinc (unmaintained since 2021)

- https://www.tinc-vpn.org/git/browse?p=tinc;a=shortlog
- ref. #405

README.md

@@ -713,7 +713,6 @@ VPN software.
 - [SoftEther](https://www.softether.org/) - Multi-protocol software VPN with advanced features. ([Source Code](https://github.com/SoftEtherVPN/SoftEtherVPN/)) `Apache-2.0` `C`
 - [sshuttle](https://github.com/sshuttle/sshuttle) - Poor man's VPN. `LGPL-2.1` `Python`
 - [strongSwan](https://www.strongswan.org/) - Complete IPsec implementation for Linux. ([Source Code](https://github.com/strongswan/strongswan)) `GPL-2.0` `C`
-- [tinc](https://www.tinc-vpn.org/) - Distributed p2p VPN. ([Source Code](https://www.tinc-vpn.org/git/tinc)) `GPL-2.0` `C`
 - [WireGuard](https://www.wireguard.com/) - Very fast VPN based on elliptic curve and public key crypto. ([Source Code](https://www.wireguard.com/repositories/)) `GPL-2.0` `C`