If you no longer need to use a project, you can easily remove it from your project usages.
Removal is complete; all references to the elements stored in the used project will be eliminated.
Before you attempt to stop using a project, make sure other users are not currently creating usages to this project.  | 
To stop using a project in your project
Select the used project and click the 
 button.
This step can be done via a shortcut menu. Right-click the project and then select Remove.  | 

The project is no longer used in your project and will disappear from the Model Browser of your project.