They started adding jQuery migrate in WordPress 3.6. Most up-to-date frontend code and plugins don’t require jquery-migrate.min.js. In most cases, this simply adds unnecessary load to your site. You can see this running if you launch Chrome Devtools console.
You can easily remove this in the perfmatters plugin by enabling the “Remove jQuery Migrate.”
We have had some reports from those using page builders and Visual Composer that this sometimes breaks images. If you see this, we recommend leaving jQuery Migrate enabled.