refactor(dotfiles): centralize Nix file names

src/dotfiles/guests.nix

@@ -1,6 +1,5 @@
 {
   inputs,
-  lib,
   root,
   specialArgs,
   repositoryModules,
@@ -276,7 +275,7 @@ let
       };
     };
 
-  names = map (path: lib.removeSuffix ".nix" (builtins.baseNameOf path)) files;
+  names = map util.removeNixSuffix files;
 in
 {
   imports = files ++ map mkGuest names;