Menu won't go away after removing plugin

I deactivated the plugin, but the custom menu is still appearing. But now it’s not only the single page I added it to, it’s all pages.

Removing the plugin completely didn’t work. In fact, deleting the custom menu itself (under Appearance > Menus) didn’t do anything, either. The menu is still appearing on all pages.

What changes did this plugin make, and how to I reverse them?

https://www.ads-software.com/plugins/ce-wp-menu-per-page/