Revert "docker: use the system dns for app containers"

This reverts commit 92bce26e22.

src/docker.js

@@ -373,6 +373,10 @@ async function createSubcontainer(app, name, cmd, options) {
     if (isAppContainer) {
         containerOptions.Hostname = app.id;
         containerOptions.HostConfig.NetworkMode = 'cloudron'; // user defined bridge network
+        // use unbound for app DNS resolution. this is a workaround for the requirement that OIDC server name has to resolve to
+        // public IP somehow skipping any /etc/hosts entries
+        containerOptions.HostConfig.Dns = ['172.18.0.1'];
+        containerOptions.HostConfig.DnsSearch = ['.'];
 
         containerOptions.NetworkingConfig = {
             EndpointsConfig: {