Remove unused makeAlert() code

lib/main.dart

@@ -31,22 +31,6 @@ void main() {
   );
 }
 
-void makeAlert(BuildContext context, String title, String message) {
-  showDialog<String>(
-    context: context,
-    builder: (BuildContext context) => AlertDialog(
-      title: Text(title),
-      content: Text(message),
-      actions: <Widget>[
-        TextButton(
-          onPressed: () => Navigator.pop(context, 'OK'),
-          child: const Text('OK'),
-        ),
-      ],
-    ),
-  );
-}
-
 Future<OpenSSHEd25519KeyPair> generateKeyPair() async {
   final algorithm = Ed25519();