matrix-conduit: Stop using the version from unstable

flake.lock

@@ -289,22 +289,6 @@
         "type": "github"
       }
     },
-    "nixpkgs-unstable": {
-      "locked": {
-        "lastModified": 1667610399,
-        "narHash": "sha256-XZd0f4ZWAY0QOoUSdiNWj/eFiKb4B9CJPtl9uO9SYY4=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "1dd8696f96db47156e1424a49578fe7dd4ce99a4",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixpkgs-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "nixpkgs_2": {
       "locked": {
         "lastModified": 1667564121,
@@ -406,7 +390,6 @@
       "inputs": {
         "deploy-rs": "deploy-rs",
         "nixpkgs": "nixpkgs_2",
-        "nixpkgs-unstable": "nixpkgs-unstable",
         "nvfetcher": "nvfetcher",
         "sops-nix": "sops-nix",
         "tlaternet-webserver": "tlaternet-webserver"