nix: clean up package

nix/shell.nix

@@ -1,15 +1,14 @@
 {
-  callPackage,
-  gopls,
+  mkShell,
   go,
-}: let
-  mainPkg = callPackage ./package.nix {};
-in
-  mainPkg.overrideAttrs (oa: {
-    nativeBuildInputs =
-      [
-        gopls
-        go
-      ]
-      ++ (oa.nativeBuildInputs or []);
-  })
+  gopls,
+  delve,
+}:
+mkShell {
+  name = "mdlinkt";
+  packages = [
+    go
+    gopls
+    delve
+  ];
+}