[css-nav-1] Update the explainer

Author: Jihye Hong

css-nav-1/explainer.md

@@ -195,30 +195,9 @@ element of the author's choosing.
 * navbeforefocus
   - Occurs before spatial or sequential navigation changes the focus.
 
-* navbeforescroll
-  - Occurs before spatial navigation triggers scrolling.
-
 * navnotarget
   - Occurs before going up the tree to search candidates in the nearest ancestor spatial navigation focus container when spatial navigation has failed to find any candidate within the current spatial navigation focus container.
 
-#### Example
-The following code changes the behavior of spatial navigation from scrolling when there is no focusable element visible, to jumping to focusable elements even when they are not visible.
-```js
-document.addEventListener("navbeforescroll", function(e) {
-    var container = e.relatedTarget;
-    var areas = container.focusableAreas({ mode: "all" });
-
-    if (areas.length == 0)) { return; }
-
-    e.preventDefault();
-    var t = e.target.spatialNavigationSearch({
-        dir: e.dir,
-        candidates: areas
-    });
-    t.focus();
-});
-```
-
 ## FAQ
 
 ### Why do you say that there is no such thing as "the order" in a visual document?