Deleting an entity type does not remove its database sequences

[tommydeboer]

How to Reproduce

1. Create an entity type with an id attribute with a sequence (follow the documentation)
2. Inspect the information_schema.sequences table in the database and locate your sequence
3. Delete the entity type

Expected behavior

The sequence is deleted from the database

Observed behavior

The sequence is not deleted from the database since there is no administration for which sequence belongs to which entity type.