If you no longer need to use a project, you can easily remove it from your project usages.
Removal can be:
Complete, after which all references to the elements stored in the used project are eliminated.
Incomplete, after which all references are preserved. Choose this method when you need to replace the used project with an equivalent project containing the same elements with slightly different content.
Before you attempt to stop using a project, make sure other users are not currently creating usages to this project.