By default elgg is not packed with push notifications. If you are seeing them in your site, some plugin or theme you are using is causing this. 

I have removed sw.js file from root folder . Please check again on all devices .

No. We don't need to check anything. YOU should check what's sending these push notification on your Elgg site. As Sarath said, Elgg sends no push notification without any additional plugin installed that provides this functionality. Disable this plugin and the push notifications should stop. I don't know what the sw.js file should be. But removing any files without knowing their purpose can easily break the site. So, you might think before installing any stuff you don't need and then asking each day a new question about something not working on your site.