Deleting an index set does not update index set overview

## Expected Behavior

Deleting an index set should close the modal and update the list

## Current Behavior

The "delete index set" modal does not close and the list does not update, until you refresh the page.

## Possible Solution

## Steps to Reproduce (for bugs)

1. Go to the index set overview
2. Open the "delete index set" modal by clicking on delete in the actions menu
3. Click on the submit button in the modal

## Context

Related to https://github.com/Graylog2/graylog2-server/pull/15155

## Your Environment

* Graylog Version: Current development version based on 5.1, does not occur with 5.1