{nixos/,}.tt-rss: drop

Per https://community.tt-rss.org/t/the-end-of-tt-rss-org/7164, it will
cease development on 2025-11-01, and since it cannot be maintained
through the release of NixOS 25.11, it is being dropped now.

nixos/modules/module-list.nix

@@ -1707,7 +1707,6 @@
   ./services/web-apps/suwayomi-server.nix
   ./services/web-apps/szurubooru.nix
   ./services/web-apps/trilium.nix
-  ./services/web-apps/tt-rss.nix
   ./services/web-apps/umami.nix
   ./services/web-apps/vikunja.nix
   ./services/web-apps/wakapi.nix