The "Subscribe to: Posts (Atom)" is a link that viewers can use to subscribe to your blogger site so they get a feed of your posts.
Atom is similar to RSS feeds. They both provide new content of websites that are followed so that updates can be viewed in a feed reader without having to periodically visit the site to find out if anything new was posted.
If you don’t want to provide this option to your readers, or if you feel the display of that option interferes with the looks of your layout, you can remove it by following these steps as of the 2018 version of Blogger:
1. Go to the “Theme” settings.
2. Click “Edit HTML”
3. Place the curser within the code box.
4. Find (CTRL-F) the following line of code and remove it:
< b:include name='feedLinks' >
5. Click on the “Save Theme” tab button.
6. Click the “Back” tab button to return from the editor.