MM-46577: Remove empty translation strings (#20876)

We replace the empty translation key with <untranslated>
which is ignored by the translation check tool.

https://mattermost.atlassian.net/browse/MM-46577

```release-note
NONE
```

Makefile

@@ -330,11 +330,11 @@ app-layers: ## Extract interface from App struct
 	$(GO) run ./app/layer_generators -in ./app/app_iface.go -out ./app/opentracing/opentracing_layer.go -template ./app/layer_generators/opentracing_layer.go.tmpl
 
 i18n-extract: ## Extract strings for translation from the source code
-	$(GO) install github.com/mattermost/mattermost-utilities/mmgotool@v0.0.0-20210721133912-8b250bf4d0f6
+	$(GO) install github.com/mattermost/mattermost-utilities/mmgotool@fdf2cd651b261bcd511a32da33dd76febedd44a8
 	$(GOBIN)/mmgotool i18n extract --portal-dir=""
 
 i18n-check: ## Exit on empty translation strings and translation source strings
-	$(GO) install github.com/mattermost/mattermost-utilities/mmgotool@v0.0.0-20210721133912-8b250bf4d0f6
+	$(GO) install github.com/mattermost/mattermost-utilities/mmgotool@fdf2cd651b261bcd511a32da33dd76febedd44a8
 	$(GOBIN)/mmgotool i18n clean-empty --portal-dir="" --check
 	$(GOBIN)/mmgotool i18n check-empty-src --portal-dir=""