How to remove "Open a pull request" warning

I’ve just started using GitHub and am facing an annoyance.
For every branch in my repository that’s not the master branch I see a yellow warning tile on top of the repository page (code tab) stating that “[Branch] had recent pushes # minutes ago” with a button “Compare & pull request” that takes me to an “Open a pull request” page. The more branches I have, the more warnings I see. My branches are not meant to be merged to master. And why in the world would I want Pull Requests when I’m the only developer of my repository? How do I get rid of these warnings?

That’s temporary, you only see it for branches that aren’t default and have had recent activity.