Update docs against 16872

Signed-off-by: wusongqing<wusongqing@huawei.com>

en/application-dev/windowmanager/application-window-stage.md

@@ -331,7 +331,6 @@ A floating window is created based on an existing task. It is always displayed i
 
    ```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 {
@@ -389,4 +388,3 @@ A floating window is created based on an existing task. It is always displayed i
        }
    };
    ```
\ No newline at end of file
-