Merge pull request #13088 from apache/fix/remove-es6-code

style: remove unexpected es6 code

Author: pissang

src/component/timeline/SliderTimelineView.js

@@ -618,8 +618,8 @@ function getViewRect(model, api) {
 }
 
 function makeIcon(timelineModel, objPath, rect, opts) {
-    const style = opts.style;
-    const icon = graphic.createIcon(
+    var style = opts.style;
+    var icon = graphic.createIcon(
         timelineModel.get(objPath),
         opts || {},
         new BoundingRect(rect[0], rect[1], rect[2], rect[3])