Remove empty external apps config

There is nothing that would activate ocis-hello as an external app, so
this can be just removed. Also it blocks the new default apps in
ocis-phoenix.

pkg/command/phoenix_ocis.go

@@ -20,8 +20,5 @@ func configurePhoenix(cfg *config.Config) *svcconfig.Config {
 		cfg.Phoenix.Tracing.Service = cfg.Tracing.Service
 	}
 
-	// disable ocis-hello extension
-	cfg.Phoenix.Phoenix.Config.ExternalApps = []svcconfig.ExternalApp{}
-
 	return cfg.Phoenix
 }