Don't delete all image style derivatives on module uninstall

Closes #3491776

webp.install

@@ -68,9 +68,4 @@ function webp_uninstall() {
       }
     }
   }
-  else {
-    /* @var \Drupal\webp\Webp $webp */
-    $webp = \Drupal::service('webp.webp');
-    $webp->deleteImageStyleDerivatives();
-  }
 }