Uninstalling properly

Hey there, I’m having a lot of trouble on my website so I’m going through a process of troubleshooting. That includes completely uninstalling my plugins to try to identify issues, and then ideally reinstalling them.

After I uninstalled Caxton, I got lots of query errors saying things like
Undefined index: "caxton/inc/wp-sdk"
I assume that the plugin didn’t uninstall properly, so how can I make sure it does so?