applets/kickoff: show sidebar highlight with switch on hover

Until recently, we had two mechanisms for drawing the sidebar ListView highlight: usually the default highlight, but sometimes we would set it as a background for specific purposes and have some logic to choose which one to use (e.g. for the flashing animation when a new favorite is added). We now use the background method for all of them, replacing the background if we need special handling. But in this switch we missed the case where the setting to switch category on hover would defer to the standard highlight, and the custom implementation removes the logic from the standard background, so we don't display any highlight if that setting is active.

Instead, remove that special handling and show the background highlight.

BUG: 521558 FIXED-IN: 6.7.1