How to remove entity type from drush?
Entity types can't be generically deleted. First of all, node is entity type and can't be deleted using node_type_delete. You can only delete content type - and that's a bundle of entity called node.

To delete bundles that belongs to other modules, module providing entity type needs to provide drush command to delete bundle. You will find that command in module's documentation. And to remove entity type altogether, you need to disable and uninstall module that provides said entity type.

An Introduction to Entities may be a good read for you now. I advise caution, because it's status is "Needs technical review", but it covers basics nicely.