If you want to remove the Microsoft Teams Banner on your SharePoint Site, the only thing you need is to set a web property on a site: TeamifyHidden=TRUE. I’ll give you some guidance below. But before you do that, consider following:
If there is already a team created for a group connected site, the prompt won’t show up. Why fix something that is not a problem? Only group owners will get the prompt, if they are few and they know what it is, it is better to let them to decide whether to create or not to create a team.