Issues not updated in the index when labels are deleted

Summary

Steps to reproduce

1. enable the feature flag for issue labels: Feature.enable(:search_issue_label_aggregation)
2. setup gdk for elasticsearch, enable advanced search, and index everything
3. add a label to an issue
4. delete the label from the project
5. watch elasticsearch.log to see if any issues are queued for indexing

What is the current bug behavior?

no issues are queued for indexing

What is the expected correct behavior?

issues with the label being deleted are queued for indexing

Possible fixes

TBD