Problem/Motivation Flag prevents deleting any entity.

Steps to reproduce Once flag is enabled, any attempt to delete an entity will result in error:

``` TypeError: Argument 1 passed to Drupal\Core\Entity\Sql\DefaultTableMapping::requiresDedicatedTableStorage() must implement interface Drupal\Core\Field\FieldStorageDefinitionInterface, null given, called in /external/src/web/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php on line 331 en Drupal\Core\Entity\Sql\DefaultTableMapping->requiresDedicatedTableStorage() (línea 521 de /external/src/web/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php)

0 /external/src/web/core/lib/Drupal/Core/Entity/Sql/DefaultTableMapping.php(331): Drupal\Core\Entity\Sql\DefaultTableMapping->requiresDedicatedTableStorage(NULL)

1 /external/src/web/core/lib/Drupal/Core/Entity/Query/Sql/Tables.php(468): Drupal\Core\Entity\Sql\DefaultTableMapping->getAllColumns('flagging')

2 /external/src/web/core/lib/Drupal/Core/Entity/Query/Sql/Tables.php(217): Drupal\Core\Entity\Query\Sql\Tables->getTableMapping('flagging', 'flagging')

3 /external/src/web/core/lib/Drupal/Core/Entity/Query/Sql/Condition.php(51): Drupal\Core\Entity\Query\Sql\Tables->addField('entity_type', 'INNER', NULL)

4 /external/src/web/core/lib/Drupal/Core/Entity/Query/Sql/Query.php(176): Drupal\Core\Entity\Query\Sql\Condition->compile(Object(Drupal\mysql\Driver\Database\mysql\Select))

5 /external/src/web/core/lib/Drupal/Core/Entity/Query/Sql/Query.php(80): Drupal\Core\Entity\Query\Sql\Query->compile()

6 /external/src/web/modules/contrib/flag/src/FlagService.php(370): Drupal\Core\Entity\Query\Sql\Query->execute()

7 /external/src/web/modules/contrib/flag/flag.module(527): Drupal\flag\FlagService->unflagAllByEntity(Object(Drupal\dexp_layerslider\Entity\Slider))

8 [internal function]: flag_entity_predelete(Object(Drupal\dexp_layerslider\Entity\Slider))

(...)

```