Supplier has been added to the Edit Product screen so you can change a Product's supplier. This will impact invoicing (such that product will be broken out onto a different supplier order) so you should not be changing a Products supplier unless you have a known reason to do so. However, there is sometimes a legitimate need to re-assign Supplier you can now accomplish this!
Steps to edit supplier
Navigate to the Products tab
Select the product you would like to reassign the supplier for
On the left hand side, click the red re-assign supplier link
Select the new supplier you would like from the dropdown menu
Click the blue save button