You can delete unused UET tags that aren't associated with conversion goals, audiences or shared with other accounts. Once a UET tag is deleted, it will no longer show in the grid. Don't know what UET is? See What is UET and how can it help me?
If a UET tag doesn't meet the requirements for deletion, you will see an error with the number of changes that weren't made. Select Show errors to see which conditions weren't met.