jQuery Migrate is included on all pages since WordPress version 3.6. It restores APIs and features that have been deprecated and/or removed in newer versions of jQuery.
To remove jQuery Migrate script from the front end of your site, you can install and activate the Remove jQuery Migrate plugin.
If you're building a theme or plugin that still requires jQuery Migrate, you should consider updating your code. To check whether your theme/plugin requires jQuery Migrate in the front end, load the development version of jQuery Migrate (jquery-migrate.js) by turning on the SCRIPT_DEBUG mode in your wp-config.php file.
define( 'SCRIPT_DEBUG', true );
The development version will generate warnings on the browser console that you can use to identify and fix problems, until you no longer need jQuery Migrate and can remove it.