Drop "host" network mode from docker compose
Drop "host" network mode from docker compose

The auto-dependency updater and all PRs now fail with the following error:
```
Cannot create container for service yarpc-go-1.10: cannot share the host's network namespace when user namespaces are enabled
```

The Docker documentation [here](https://docs.docker.com/engine/security/userns-remap/) indicates that user namespaces conflict with when `network_mode: "host"`. We're unsure why, but user namespaces seems to have been enabled on BuildKite which directly conflicts with our `docker-compose` setup.

This drops the `network_mode` which was previously set to `"host"`. There will be no impact on current tests since no tests do not need to communicate to other containers.

yarpc/yarpc-go,yarpc/yarpc-go