Sanitizing remains of uninstalled plugins

For a while I’ve used a plugin that is outdated. I did deactivate it and the uninstalled it. However, when looking at my files through the FTP I can see that the plugin name is still in my directory, together with my other plugins that is still active. I see this for both the plugins Realaccessability and Woo Commerce. I’m not using any of them, though I have used Realaccessability before.

Yesterday I received the error:

Recently an error occurred while creating the CSS / JS minify cache: File “/…./…./public_html/wp-content/plugins/real-accessability/real-accessability.js” doesn’t exist.

This was actually what made me discover the “leftovers” of earlier plugins.

My question is if just deleting these leftover subdirectories/plugins via my cPanel or FTP is a secure way of deleting the leftovers? Or should this be removed through a appropriate uninstalling procedure?. Or is there maybe a plugin I can use for this (I’ve searched but not found any).

I’ve found several plugins for cleaning up my database, and I’m currently using WP Optimize, so my question is not regarding the cleaning up of my database/tables. My question (before attempting this) is if I could just go through my plugins and delete any files/subdirectories (leftovers) with plugins I’ve most certainly deactivated and uninstalled through the normal deactivation and uninstallation.

(I realize that the error code which I receive not necessarily has anything to do with my question, as it could be a caching problem/css/js-minifying issue.)