Delete unused classes in autotagger.module file

Tag event doesn't exist anymore, please remove this line.

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Form\FormStateInterface;
use Drupal\node\NodeInterface;
use Drupal\node\Entity\NodeType;
use Drupal\taxonomy\TermInterface;
use Drupal\Core\Entity\ContentEntityInterface;