get agenix package from flake

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": {