Below are the steps necessary to hide an existing relation from displaying throughout your project.
Within the 'Schema Editor', ensure "Relations" is highlighted in the 'Select' tab of the left sidebar.
Locate the relation you'd like to hide and click anywhere within the relation's displayed row, as shown below:
The view will update to display an edit form where you can change the 'Hidden' attribute of the existing relation to "Yes" to hide that relation from displaying throughout your project.
Click on the 'Save' button located on the toolbar to persist your changes to your project's database schema.