update docs against 8161

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

en/application-dev/windowmanager/display-guidelines.md

@@ -10,12 +10,11 @@ For details about the APIs, see [Display](../reference/apis/js-apis-display.md).
 
 ## How to Develop
 
-Call **getDefaultDisplay(): Promise<Display>** to obtain the default display object. An example code snippet is as follows:
+Call `getDefaultDisplay(): Promise<Display>` to obtain the default display object. An example code snippet is as follows:
 
 ```js
 import display from '@ohos.display' // Import the module.
 
-let disp; // disp is used to save the default display object.
 display.getDefaultDisplay().then((disp) => {
 	console.log('display.getDefaultDisplay success, display :' + JSON.stringify(disp));
 }, (err) => {