To stop seeing a supplier and its items in the documents, you can disable it. But there is no possibility to delete a supplier entirely, as it already keeps some history logs in the system.  

To disable a supplier, please follow these steps:

        1. Please go to the supplier management tab and click on manage suppliers.

        2. Click on "show a filter" and find the supplier that you want to disable.

        3. Then in the Action column, click on the "edit" button.

        4. You can click on the "Enable" switcher in the General Info to disable the enabled supplier or vice versa.

        5. Then go to the bottom of the page and click on the "Update" button to save the changes.

Now your supplier is disabled. 

You can always enable it again, just check this article.