Don't show unnecessary root authentication message

This message is pointless because the user will find out that they need to authenticate when they click the "Apply" button anyway. Showing the user this information ahead of time just contributes to visual clutter when it is even shown.

However the message hasn't even been shown for at least 9 months due to an intentional change in header height calculation to make the KCM header height always match the height of the category/subcategory sidebar header height. This had the side effect of entirely or mostly cutting off the authentication message. With the current design, there is no way to fix this without regressing the header alignment fix, and the message is pretty much unnecessary anyway, so the simplest solution is to not show it at all.

BUG: 434113 FIXED-IN: 5.24

Before	After

observe the second line of text that you can select by triple-clicking in the "Before" view. Details of how it looks when unselected:

cc @teams/vdg