[Sidebar] Remove unneeded highlighted: properties

BasicListItem gives us this for free; no need to set it again ourselves.

sidebar/package/contents/ui/CategoriesPage.qml

@@ -169,7 +169,6 @@ Kirigami.ScrollablePage {
                     categoryView.positionViewAtIndex(index, ListView.Contain);
                 }
             }
-            highlighted: categoryView.currentIndex == index
             Keys.onEnterPressed: clicked();
             Keys.onReturnPressed: clicked();
             showArrow: {

sidebar/package/contents/ui/SubCategoryPage.qml

@@ -155,7 +155,6 @@ Kirigami.ScrollablePage {
                     onCurrentIndexChanged: subCategoryView.positionViewAtIndex(index, ListView.Contain);
                 }
             }
-            highlighted: systemsettings.activeSubCategoryRow == index
             Keys.onEnterPressed: clicked();
             Keys.onReturnPressed: clicked();
         }