How can you remove the glossary widget in Captivate 7?

It will probably be on one of the first slides and hidden in the Tmeline (and probably in Output, if you can show/hide that interaction on each slide which is a common work flow).

It's probably sitting on one of the early slides in the project timed to Display for Rest of Project and set to NOT Visible in Output so that it gets shown at runtime when the user clicks something.

But setting an object to Rest of Project usually means it is then visible in Edit mode on all other slides after that, which can be very annoying when building the course.  So most authors will turn it off on the timeline to avoid it getting in the way.

Look for objects on those slides that have a red X beside their item on the timeline.  That might be your Glossary widget.