A deleted content type leaves behind a bunch of unused persistent variables. With all core modules enabled, I found these:
- additional_settings__active_tab_NODETYPE
- language_content_type_NODETYPE
- menu_options_NODETYPE
- menu_parent_NODETYPE
- node_options_NODETYPE
- node_preview_NODETYPE
- node_submitted_NODETYPE
- save_continue_NODETYPE
The menu variables also don't get deleted when uninstalling menu module.
I'm filing this against 7.x since the variable system is going away in 8.x. Patch to follow.