deleteFieldSchemaData example

// Delete entity and field tables.     $table_names = $this->getTableNames($entity_type, $this->fieldStorageDefinitions, $this->getTableMapping($entity_type));
    foreach ($table_names as $table_name) {
      if ($schema_handler->tableExists($table_name)) {
        $schema_handler->dropTable($table_name);
      }
    }

    // Delete the field schema data.     foreach ($this->fieldStorageDefinitions as $field_storage_definition) {
      $this->deleteFieldSchemaData($field_storage_definition);
    }

    // Delete the entity schema.     $this->deleteEntitySchemaData($entity_type);
  }

  /** * {@inheritdoc} */
  public function onFieldableEntityTypeCreate(EntityTypeInterface $entity_type, array $field_storage_definitions) {
    // When installing a fieldable entity type, we have to use the provided