Remove the Vaadin Router patch

[abdonrd]

The Vaadin Router doesn't help us to restore scroll position on navigation.
There is already an issue about it: vaadin/router#43

Meanwhile, for now, we have created a simple patch to deal with it: now when you perform a click event, the scroll will be reset to the top position.

But we wish we could find a good solution soon.

We already mentioned it here:
https://github.com/IBM/pwa-lit-template#things-to-be-aware

[abdonrd]

They merge this vaadin/router#547, so we can remove it when they release a new version.