Wordpress - Should I remove install.php and install-helper.php?

No, there is no security risk. Both files do sanity checks before anything happens.

If WordPress is already installed:

• install-helper.php returns just a blank page.
• install.php says WordPress is installed and you should log in:

You can forbid access to both files with a simple rule in your .htaccess above the permalink rules:

RedirectMatch Permanent wp-admin/install(-helper)?\.php /

This will redirect all requests to these files to the home page.