There is no way to delete a content type of module built with the module builder, even if all configuration for this type are deleted and pages removed. The removal of pages can solve the problem to make the module unacessible and if this type will no longer be used.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items