Issue #3297233: Remove @todo about implementing ConfigurableInterface

None of the methods in this interface are used.

src/Plugin/FillPdfActionPluginInterface.php

@@ -16,8 +16,6 @@ use Drupal\Core\Executable\ExecutableInterface;
  *
  * They may also have side effects, such as saving a file to the file system.
  * They must not, however, end the request.
- *
- * @todo Extend ConfigurableInterface once drupal:8.6.x is no longer supported.
  */
 interface FillPdfActionPluginInterface extends PluginInspectionInterface, DependentPluginInterface, ContainerFactoryPluginInterface, ExecutableInterface {