refactor(nix): removed redundandt let in + formatting

nix/default.nix

@@ -13,17 +13,15 @@
   wayland-scanner,
   xcbutilwm,
   xwayland,
-  enableXWayland ? true,
   meson,
   ninja,
   scenefx,
   wlroots_0_19,
   libGL,
-}: let
+  enableXWayland ? true,
+}:
+stdenv.mkDerivation {
   pname = "mango";
-in
-  stdenv.mkDerivation {
-    inherit pname;
   version = "nightly";
 
   src = builtins.path {
@@ -73,4 +71,4 @@ in
     maintainers = [];
     platforms = lib.platforms.unix;
   };
-  }
+}