docs(realtime): remove duplicate tab for dart (#28969)

docs: remove repeated tab for dart

apps/docs/content/guides/realtime/presence.mdx

@@ -82,22 +82,6 @@ SUPABASE_KEY = '<your-anon-key>'
 supabase = create_client(SUPABASE_URL, SUPABASE_KEY)
 ```
 
-</TabPanel>
-<TabPanel id="dart" label="Dart">
-
-```dart
-void main() {
-  Supabase.initialize(
-    url: 'https://<project>.supabase.co',
-    anonKey: '<your-anon-key>',
-  );
-
-  runApp(MyApp());
-}
-
-final supabase = Supabase.instance.client;
-```
-
 </TabPanel>
 </Tabs>