Rabbit Hole Node creates garbage variables when saving a node type form

tl;dr: When saving a node type form Rabbit Hole's form altering will cause additional garbage variables to be saved to the DB that are not used anywhere.

When editing a node type:

1. rh_node alters the node type form and calls rabbit_hole_form().
2. rabbit_hole_form() adds several fieldsets without #tree = TRUE. Child elements will therefore have their values added to the form root.
3. rabbit_hole_form() adds multiple #value elements to the form to pass along internal values. These are:
   
   • rh_module
   • redirect_setting_name
4. When submitting the form, node_type_form_submit() will take any excess values from the root level, suffix their names with the node type name and save the resulting key as variable. This produces two garbage variables per node type that are never requested or reused.