get agenix package from flake

flake.nix

@@ -36,7 +36,7 @@
           packageOverrides = pkgs:
             let sources = import ./npins;
             in {
-              agenix = (import sources.agenix { inherit pkgs; }).agenix;
+              agenix = agenix.packages.${config.nixpkgs.hostPlatform.system}.default;
               nur = (import sources.nur { inherit pkgs; });
               vscode-extensions = (import sources.nix-vscode-extensions).extensions.x86_64-linux; # TODO: This should check the host architecture
             };

npins/sources.json

@@ -1,20 +1,5 @@
 {
   "pins": {
-    "agenix": {
-      "type": "GitRelease",
-      "repository": {
-        "type": "GitHub",
-        "owner": "ryantm",
-        "repo": "agenix"
-      },
-      "pre_releases": false,
-      "version_upper_bound": null,
-      "release_prefix": null,
-      "version": "0.15.0",
-      "revision": "564595d0ad4be7277e07fa63b5a991b3c645655d",
-      "url": "https://api.github.com/repos/ryantm/agenix/tarball/0.15.0",
-      "hash": "01dhrghwa7zw93cybvx4gnrskqk97b004nfxgsys0736823956la"
-    },
     "nix-vscode-extensions": {
       "type": "Git",
       "repository": {