If you want to remove all the restricted posts from listing in the RSS feed of your website, you should install an add-on that you can download here.
Once installed and activated, head to Restrict Settings -> General tab and you will notice a new option as shown in the screenshot below:
If you set this option to YES, this will hide from the RSS feed all the posts that have any restriction set. Basically, only the posts that are set to be visible to Everyone will be listed in the RSS feed.
However, for now, this feature doesn’t work for global protected categories and post types because that functionality would be very “expensive” for any server.