Remove xip.io hack

After we proxy API requests through the server-side-rendered frontend
there is no need to use xip.io anymore. However, if you "join" services
to a named network at arbitrary times, the DNS of docker-compose only
works if you assign a name to the container. Thus I left `backend` as a
container name.

docker-compose.override.yml

@@ -2,7 +2,6 @@ version: "3.7"
 
 services:
   backend:
-    container_name: backend.127.0.0.1.xip.io
     volumes:
       - .:/nitro-backend
       - /nitro-backend/node_modules

docker-compose.yml

@@ -2,6 +2,7 @@ version: "3.7"
 
 services:
   backend:
+    container_name: backend
     image: humanconnection/nitro-backend:latest
     build: .
     networks: