Revert "DefaultListItemBackground: use outline only to show focus"
This reverts commit 2e548736.
This kind of change needs to be coordinated with Plasma, Breeze, and our GTK style. If not, we get an inconsistent UI that doesn't look great. Realistically I lack both the time and expertise to make those changes. So revert for now until those changes are also prepared, either by myself or others.
The before/after pics are the reverse of the ones in !349 (merged).