The following message is displayed on admin bar:

jQuery Migrate(Previously known: 4 discovered on this page:(0)

jQuery Migrate is used to preserve the compatibility of   jQuery code developed for versions of jQuery older than 1.9.  The message states that there are 4 instances of deprecated functions being used.

The message can safely be ignored.  However, jQuery Migrate cannot be safely removed without fixing the warning messages.

For more info:

What is Migrate.js – Why and How to Remove jQuery Migrate from WordPress