Clean up overlays and remove obsolete dependencies

overlays/patches/prometheus/default.nix

@@ -0,0 +1,17 @@
+{ prometheus }:
+prometheus.overrideAttrs (
+  old:
+  let
+    assets = old.passthru.assets.overrideAttrs (assetsOld: {
+      patches = (assetsOld.patches or [ ]) ++ [ ./complete-test-parsing.patch ];
+    });
+  in
+  {
+    postPatch = builtins.replaceStrings [ "${old.passthru.assets}" ] [ "${assets}" ] (
+      builtins.unsafeDiscardStringContext old.postPatch
+    );
+    passthru = old.passthru // {
+      inherit assets;
+    };
+  }
+)