Revert "readme: Add nixos.asia tutorial series (#223)"

This reverts commit 56539bc, in keeping
with the `nix-community` ban of @srid.

README.md

@@ -52,7 +52,6 @@
 * [Nix Shorts](https://github.com/alper/nix-shorts) - A collection of short notes about how to use Nix, updated for Nix Flakes.
 * [nix.dev](https://nix.dev/) - An opinionated guide for developers about getting things done using the Nix ecosystem.
 * [NixOS & Flakes Book](https://github.com/ryan4yin/nixos-and-flakes-book) - An unofficial and opinionated NixOS & Flakes book for beginners.
-* [NixOS Asia Tutorial Series](https://nixos.asia/en/tutorial) - A series of high-level tutorials on using Nix Flakes, NixOS, home-manager, etc.
 * [Tour of Nix](https://nixcloud.io/tour) - An online interactive tutorial on Nix language constructs.
 * [Wombat's Book of Nix](https://mhwombat.codeberg.page/nix-book/) - A book-length introduction to Nix and flakes.
 * [Zero to Nix](https://zero-to-nix.com/) - A flake-centric guide to Nix and its concepts created by Determinate Systems to quickly onboard beginners.