neovim: test pure lua dependencies (#8991)

a revert of https://github.com/nix-community/home-manager/pull/8959 since we now relies on nixpkgs wrapper for that.

adding a test to avoid regressions. Choosing  telescope as starting point is https://github.com/nix-community/home-manager/issues/8787

I find the nmt test setup lacking: it doesnt set $PATH or $HOME (nvim
will error when it can't write into $HOME).

modules/programs/neovim.nix

@@ -441,8 +441,8 @@ in
           withNodeJs = cfg.withNodeJs || cfg.coc.enable;
           plugins = nixpkgsCompatiblePlugins;
 
-          extraLuaPackages = lp: cfg.extraLuaPackages lp ++ vimPackageInfo.luaDependencies;
           inherit (cfg)
+            extraLuaPackages
             extraName
             withPython3
             withRuby
@@ -521,7 +521,6 @@ in
               ''
             else
               null;
-
         in
         lib.mkMerge [
           (lib.mkIf wrapperHasUserConfig (