Simplify sorting method

aleksis/apps/lesrooster/frontend/components/lesson_raster/LessonRaster.vue

@@ -285,9 +285,8 @@ export default {
       return this.items
           ?.sort(
               (a,b) =>
-              60 * 60 * (parseInt(a.timeStart.slice(0, 2)) - parseInt(b.timeStart.slice(0, 2)))
-              + 60 * (parseInt(a.timeStart.slice(3, 5)) - parseInt(b.timeStart.slice(3, 5)))
-              + parseInt(a.timeStart.slice(6, 8)) - parseInt(b.timeStart.slice(6, 8))
+              parseInt(a.timeStart.replace(":", ""))
+              - parseInt(b.timeStart.replace(":", ""))
           )  || [];
     },
     columns() {