nix: simplify isDarwin lib check

Signed-off-by: strawberry <strawberry@puppygock.gay>

nix/pkgs/main/default.nix

@@ -66,11 +66,14 @@ commonAttrs = {
       # right thing here.
       pkgsBuildHost.rustPlatform.bindgenHook
   ]
+  ++ lib.optionals stdenv.isDarwin [
       # https://github.com/NixOS/nixpkgs/issues/206242
-  ++ lib.optionals stdenv.isDarwin [ libiconv ]
+      libiconv
+
       # https://stackoverflow.com/questions/69869574/properly-adding-darwin-apple-sdk-to-a-nix-shell
       # https://discourse.nixos.org/t/compile-a-rust-binary-on-macos-dbcrossbar/8612
-  ++ lib.optionals stdenv.isDarwin [ pkgsBuildHost.darwin.apple_sdk.frameworks.Security ];
+      pkgsBuildHost.darwin.apple_sdk.frameworks.Security
+    ];
  };
 in