Really Simple SSL does not change URL’s in your database, other than the home_url, which has been reverted to http when you deactivated.
If you have https URL’s on your site, you have probably added content to your site while your site was on https. The default WordPress behaviour is then to add URl’s and images with https URL’s, which is what you are seeing now.
If you use a plugin like Yoast, this plugin will add a canonical URL to your pages that should prevent any duplicate content. For further information on this please contact Yoast support.
To replace your URL’s to http, you can do a search and replace with the better search and replace plugin.