If you no longer need to reference and manage a repository (or repository group) you can remove the repository reference or repository group from the sidebar of your document.
Important: Removing a repository just removes the reference to the repository. It doesn't actually move the folder of files to the trash, or remove the repository from the server. However, when deleting a local repository, you are given the option of moving the actual repository (the folder of files on your machine) to the trash. Choose this option with care.