fix: fixed custom directives migration guide

Author: NataliaTepluhina

src/guide/migration/custom-directives.md

@@ -10,7 +10,6 @@ badges:
 Here is a quick summary of what has changed:
 
 - API has been renamed to better align with component lifecycle
-- Custom directives will be controlled by child component via `v-bind="$attrs"`
 
 For more information, read on!
 
@@ -103,26 +102,6 @@ mounted(el, binding, vnode) {
 }
 ```
 
-## Implementation Details
-
-In Vue 3, we're now supporting fragments, which allow us to return more than one DOM node per component. You can imagine how handy that is for something like a component with multiple `<li>` elements or the children elements of a table:
-
-```html
-<template>
-  <li>Hello</li>
-  <li>Vue</li>
-  <li>Devs!</li>
-</template>
-```
-
-As wonderfully flexible as this is, we can potentially encounter a problem with a custom directive that could have multiple root nodes.
-
-As a result, custom directives are now included as part of a virtual DOM node’s data. When a custom directive is used on a component, hooks are passed down to the component as extraneous props and end up in `this.$attrs`.
-
-This also means it's possible to directly hook into an element's lifecycle like this in the template, which can be handy when a custom directive is too involved:
-
-```html
-<div @vnodeMounted="myHook" />
-```
-
-This is consistent with the attribute fallthrough behavior, so when a child component uses `v-bind="$attrs"` on an inner element, it will apply any custom directives used on it as well.
+:::warning
+With [fragments](/guide/migration/fragments.html#overview) support, components can potentially have more than one root nodes. When applied to a multi-root component, directive will be ignored and the warning will be thrown.
+:::