feat(server): Remove into_service api

[tottoto]

Removes into_service() api. This is the same as the one composed of the layers and the Routes.

[djc]

So how would you spell this in 0.13?

[tottoto]

What is the purpose? Should this api be kept in 0.13?

[djc]

I'm asking what the replacement looks like, in order to better understand how much boilerplate this call is hiding.

[tottoto]

I see. In the case where this API is used, users can build Routes in advance, so they can set some layers to the Routes with some means, for example tower's ServiceBuilder.

[djc]

I understand -- do you have a code snippet showing what that would look like?

[tottoto]

The following is an example if using tower's ServiceBuilder:

let routes = Routes::new(service()).prepare();

let service = tower::ServiceBuilder::new()
    .layer(layer())
    .service(routes);