Useless "Back" button

**Version:**
 - listmonk: [eg: v3.0.0]

I noticed that Confirmation page and Unsubscribe page contain "Back" button that doesnt do anything.

<img width="589" alt="image" src="https://github.com/knadh/listmonk/assets/55597/0bbab4f1-8a27-4a54-8ff2-bd3d97f7aad2">
<img width="634" alt="image" src="https://github.com/knadh/listmonk/assets/55597/3e0f7447-cd04-46e6-ae20-1e1738d2eef8">

