Remove user stories from nav.adoc

• Getting started with an example data source
• https://github.com/jstaffor/mobile-docs/blob/master/modules/ROOT/pages/_partials/sync/server-getting-started-with-an-example-data-source.adoc
• Deploying your app built using the data sync framework to an environment
• https://github.com/jstaffor/mobile-docs/blob/master/modules/ROOT/pages/_partials/sync/server-deploying-your-app-built-using-the-data-sync-framework-to-a-development-environment.adoc
• Creating a voyager server container image for use with OpenShift
• https://github.com/jstaffor/mobile-docs/blob/master/modules/ROOT/pages/_partials/sync/creating-a-voyager-server-container-image-for-use-with-openshift.adoc