Delete a field and its instances.
drush field-delete
field_name : Name of field to delete.
--bundle : Only delete the instance attached to this bundle. If omitted, admin can choose to delete one instance or whole field.
--entity_type : Disambiguate a particular bundle from identically named bundles. Usually not needed.
Delete the city field and any instances it might have.
field-delete city
Delete the city instance on the article bundle
field-delete city --bundle=article