There are a couple of ways to remove a supplier from an existing supplier panel. These are detailed below.
When viewing the details for the Supplier Panel there will be an Action icon to Remove Supplier next to each supplier listed under Panel Members. Click on this and confirm to remove the supplier from the Supplier Panel.
When viewing the details of a supplier there is an Action icon to Remove Supplier next to each Supplier Panel listed under Supplier Panel Memberships. Click on this and confirm to remove the supplier from the Supplier Panel.