delete unuse import

Signed-off-by: Nleafly2021 <figo.yefei@huawei.com>
Change-Id: I6f79893216425a6301795c6973ac05b6e2f6c1b6

zh-cn/application-dev/windowmanager/application-window-stage.md

@@ -320,7 +320,6 @@ export default class EntryAbility extends UIAbility {
 
    ```ts
    import UIAbility from '@ohos.app.ability.UIAbility';
-   import ExtensionContext from '@ohos.app.ability.ServiceExtensionAbility';
    import window from '@ohos.window';
    
    export default class EntryAbility extends UIAbility {