fix(nvim): conflict with using global packages

Now it is an error to override the pkgs if global packages are being
used.

flake-modules/nixos-modules.nix

@@ -2,17 +2,12 @@
 {
   flake.nixosModules =
     let
-      nvim-config =
-        { pkgs, ... }:
-        {
-          imports = [
-            inputs.nixvim.homeManagerModules.nixvim
-            (import ../nvim {
-              inherit (inputs) unstable;
-              inherit (pkgs) system;
-            })
-          ];
-        };
+      nvim-config = {
+        imports = [
+          inputs.nixvim.homeManagerModules.nixvim
+          ../nvim
+        ];
+      };
       homeManagerModuleSandalone = import ../home {
         inherit nvim-config;
         inherit (inputs) stylix;

flake-modules/nvim.nix

@@ -3,19 +3,15 @@
   flake.overlays.nixvim = inputs.nixvim.overlays.default;
 
   perSystem =
-    { pkgs, system, ... }:
+    { system, ... }:
     let
       nixvimLib = inputs.nixvim.lib.${system};
       nixvim = inputs.nixvim.legacyPackages.${system};
       testNvimModule = nixvimLib.check.mkTestDerivationFromNixvimModule;
       nvimModule = extraConfig: {
-        inherit pkgs;
-        extraSpecialArgs = {
-          inherit (inputs) unstable;
-          inherit system;
-        };
+        pkgs = inputs.unstable.legacyPackages.${system};
         module = {
-          imports = [ (import ../nvim/standalone.nix { standalone = true; }) ];
+          imports = [ ../nvim/standalone.nix ];
           config = extraConfig;
         };
       };